DR. MATTHEW CRAIG WILLIAMS MD
NPI 1326626797
Psychiatry & Neurology - Child & Adolescent Psychiatry in Mill Valley, CA

NPI Status: Active since March 29, 2021

Contact Information

655 REDWOOD HWY FRONTAGE RD STE 261
MILL VALLEY, CA
ZIP 94941
Phone: (415) 381-1690

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  • Individual
  • Male
  • Years of Experience 5
  • Psychiatry & Neurology
  • Child & Adolescent Psychiatry
  • Accepts Medicare Approved Payment
  • PECOS Enrolled

About MATTHEW WILLIAMS

This page provides the complete NPI Profile along with additional information for Matthew Williams, a provider established in Mill Valley, California with a medical specialization in Psychiatry & Neurology, focusing in child & adolescent psychiatry and more than 5 years of experience. He graduated from Georgetown University School Of Medicine in 2021. The healthcare provider is registered in the NPI registry with number 1326626797 assigned on March 2021. The practitioner's primary taxonomy code is 2084P0804X with license number A186478 (CA). The provider is registered as an individual and his NPI record was last updated June 2026.

NPI
1326626797
Provider Name
DR. MATTHEW CRAIG WILLIAMS MD
Gender
Male
Entity Type
Individual
Location Address
655 REDWOOD HWY FRONTAGE RD STE 261 MILL VALLEY, CA 94941
Location Phone
(415) 381-1690
Mailing Address
655 REDWOOD HWY FRONTAGE RD STE 261 MILL VALLEY, CA 94941
Mailing Phone
(415) 381-1690
Medical School Name
GEORGETOWN UNIVERSITY SCHOOL OF MEDICINE
Graduation Year
2021
Is Sole Proprietor?
No
Enumeration Date
03-29-2021
Last Update Date
06-09-2026
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Specialty - Primary Taxonomy

The NPI enumerator requires providers to submit at least one taxonomy code. A taxonomy code is a unique 10-character code that describes the healthcare provider type, classification, and the area of specialization. There could be only one primary taxonomy code per NPI record. For individual NPIs the license data is associated to the taxonomy code.

Classification

Psychiatry & Neurology Child & Adolescent Psychiatry

Taxonomy Code
2084P0804X
Type
Allopathic & Osteopathic Physicians
License No.
A186478
License State
CA
Taxonomy Description
Child & Adolescent Psychiatry is a subspecialty of psychiatry with additional skills and training in the diagnosis and treatment of developmental, behavioral, emotional, and mental disorders of childhood and adolescence.

Secondary Taxonomies

The provider has reported to the NPI enumerator additional taxonomy codes. Multiple taxonomy codes may represent subspecialties or other areas of specialization the provider maybe licensed to practice.

No. Taxonomy Code Type Classification /
Specialization
License No. (State)
12084P0800XAllopathic & Osteopathic Physicians

Psychiatry & Neurology
Psychiatry

A186478 (CA)

Medicare Participation & PECOS Enrollment Status

Matthew Williams is registered with Medicare and accepts claims assignment, this means the provider accepts the approved amount for the cost of rendered services as full payment. Participating providers may not charge beneficiaries more than the approved amount for their services. Please keep in mind that beneficiaries still have to pay a coinsurance or copayment amount for a visit or service.

Matthew Williams is enrolled in PECOS and is eligible to order or refer health care services for Medicare patients. The provider is eligible to order or refer: Part B Clinical Laboratory and Imaging, Durable Medical Equipment (DME), a Home Health Agency (HHA) and Power Mobility Devices.

What is PECOS?
PECOS is the online Medicare enrollment management system or Provider, Enrollment, Chain and Ownership System. The PECOS system is a database of providers who have registered with CMS as providers or suppliers. PECOS is the primary source of information about verified Medicare professionals. Providers that want to participate in this program need to enroll in PECOS with their NPI number to avoid denied claims.

  • Is the provider registered in PECOS? Yes

  • PECOS PAC ID: 6709259203

    What is the PECOS Associate Control ID?
    A PAC ID is a unique 10-digit number assigned to an individual or organization healthcare provider in PECOS. The PAC ID is used to link together all the provider information, like tax identification numbers and organizational names. A PAC ID can be connected to multiple Enrollment IDs if an individual or organization has enrolled in PECOS more than once.

  • PECOS Enrollment ID: I20231109003422

    What is the Provider Enrollment ID?
    The Enrollment ID is a unique alphanumeric 15-digit code assigned to each new provider's PECOS enrollment application. The Enrollment ID is used to link together all the provider enrollment information like enrollment type, state, provider specialty, and reassignment of benefits.

  • Accepts Medicare Assignment? Yes

    What does it mean "accepts medicare assignment"?
    When a provider accepts Medicare assignment, the provider agrees to be paid directly by Medicare and to accept the payment amount approved by Medicare. Additionally, the provider agrees to not bill patients for more than the Medicare deductible and coinsurance amounts.
    A provider who doesn't accept assignment may charge you up to 15% over the Medicare-approved amount. This is known as the limiting charge. You may have to pay this amount, or it may be covered by another insurer.

  • Eligible to Order or Refer Part B Clinical Laboratory and Imaging: Yes

  • Eligible to Order or Refer Durable Medical Equipment (DMEPOS): Yes

  • Eligible to Order or Refer a Home Health Agency (HHA): Yes

  • Eligible to Order or Refer Power Mobility Devices: Yes

Areas of Expertise

The following services and procedures, recently provided to Medicare patients, illustrate the range of care this provider offers. This list reflects the variety of services available to all patients visiting the practice and is based on 2022 Medicare dataset. In general, the more frequently a provider treats specific conditions or performs particular procedures, the more experienced they become in addressing similar patient needs. The provider has delivered many of the services listed below to Medicare patients. Please note that this list does not include services provided to patients who are not covered by Medicare.

Psychiatric diagnostic evaluation with medical services

A psychiatric diagnostic evaluation with medical services is a comprehensive assessment. It includes a detailed examination of your mental health and physical wellbeing, as well as your personal and family history. This evaluation aids in creating an effective treatment plan.

This service was performed 15 times for 15 patients

Psychotherapy with evaluation and management visit, 30 minutes

Psychotherapy with evaluation and management is a 30-minute session where a mental health professional talks with you about your concerns and feelings. They assess your mental health, provide support, and manage your treatment plan to help improve your well-being.

This service was performed 73 times for 40 patients

Subsequent hospital care with moderate levelof medical decision making, if using time, at least 50 minutes

Follow-up hospital inpatient care per day typically involves a 35-minute check-up by your healthcare provider. This service includes monitoring your health progress, adjusting your treatment plan if needed, and answering any questions you may have about your condition or care.

This service was performed 80 times for 40 patients

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NPI NPI Number Validation

How NPI Validation Works

The NPI validation process uses the ISO-standard Luhn algorithm, a mathematical "handshake", to ensure that a provider's 10-digit ID is authentic and free of common typing errors.

To verify the NPI 1326626797, we treat the final digit (7) as the Check Digit—the target answer we need to reach. The process begins by taking the first nine digits and adding a constant value of 24, which accounts for the "80840" prefix required for all U.S. health identifiers. We then double every other digit starting from the right and sum the individual digits of those results together. For this specific NPI, that total comes to 63. The final step is to find the difference between that total and the next multiple of ten (70 - 63 = 7).

Digit-by-digit view

Use the first nine digits for the calculation. Starting from the right, double every other digit. The last digit is the check digit and is not part of the calculation.

Pos 1
1
Doubled → 2
Pos 2
3
Unchanged
Pos 3
2
Doubled → 4
Pos 4
6
Unchanged
Pos 5
6
Doubled → 12 → 1 + 2
Pos 6
2
Unchanged
Pos 7
6
Doubled → 12 → 1 + 2
Pos 8
7
Unchanged
Pos 9
9
Doubled → 18 → 1 + 8
Check
7
Target digit
Regular digit Doubled digit Check digit

Step 1: Double every other digit from the right

Starting with the rightmost digit of the first nine digits, double every other value. If doubling creates a two-digit number, add those digits together.

1 → 2 2 → 4 6 → 12 → 3 6 → 12 → 3 9 → 18 → 9

Step 2: Add all digits plus the NPI constant

Add the transformed values, the unchanged digits, and the constant 24.

2 + 3 + 4 + 6 + 1 + 2 + 2 + 1 + 2 + 7 + 1 + 8 + 24 = 63

Step 3: Find the amount needed to reach the next multiple of 10

The next multiple of ten after 63 is 70. The difference is the calculated check digit.

70 - 63 = 7
This NPI is valid
The calculated check digit is 7, which matches the last digit of 1326626797.

Other Providers at the Same Location


The following 1 provider is registered at the same or a nearby location.

Psychiatry & Neurology (Child & Adolescent Psychiatry)
655 REDWOOD HWY FRONTAGE RD STE 261
MILL VALLEY, CA 94941

Frequently Asked Questions

The NPI number assigned to this healthcare provider is 1326626797, enumerated as an "individual" on March 29, 2021.

The provider is located at 655 REDWOOD HWY FRONTAGE RD STE 261 MILL VALLEY, CA 94941 and the phone number is (415) 381-1690.

Psychiatry & Neurology with taxonomy code 2084P0804X and a focus in Child & Adolescent Psychiatry.