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DR. WILLIAM JAMES GIESEN M.D.
NPI 1124104724
Internal Medicine in Darien, CT

Active since October 27, 2006PECOS EnrolledAccepts Medicare AssignmentCLIA 07D0716667 · Waiver
1500 POST RD., DARIEN, CT 06820(203) 655-2516(203) 656-3665 Get Directions Write a Review

NPPES record last updated: May 9, 2016. Verified against the NPPES registry weekly; last sync: August 02, 2026.

About Dr. William James Giesen M.d. NPPES

Official registry information on file with the National Plan and Provider Enumeration System.

DR. WILLIAM JAMES GIESEN M.D. (NPI 1124104724) is an individual internal medicine provider in Darien, Connecticut, licensed in Connecticut (CT023721) and active in the NPI registry since October 2006. He is enrolled in Medicare PECOS, holds a CLIA Waiver certificate valid through September 9, 2026, and is a graduate of Georgetown University School Of Medicine (1975).

NPPES Registry Identity

NPI1124104724
Entity TypeIndividualMale
Primary Taxonomy207R00000X
Provider Legal NameDR. WILLIAM JAMES GIESENCredential: M.D.
Location Address1500 POST RD.Darien, CT 06820
Mailing Address1500 Post RdDarien, CT 06820 · (203) 655-2516 · Fax (203) 656-3665
Phone(203) 655-2516
Fax(203) 656-3665
Sole ProprietorYes
Medical School CMSGeorgetown University School Of MedicineGraduated 1975
Enumeration DateOctober 27, 2006
Last NPPES UpdateMay 9, 2016
✔ NPI 1124104724 is a valid, active identifier and passes the ISO check-digit test.

Specialties & Licenses

★ Primary SpecialtyInternal MedicineAllopathic & Osteopathic Physicians
Taxonomy Code207R00000X
License✔ Licensed in CT · CT023721
Definition
A physician who provides long-term, comprehensive care in the office and the hospital, managing both common and complex illness of adolescents, adults and the elderly. Internists are trained in the diagnosis and treatment of cancer, infections and diseases affecting the heart, blood, kidneys, joints and digestive, respiratory and vascular systems. They are also trained in the essentials of primary care internal medicine, which incorporates an understanding of disease prevention, wellness, substance abuse, mental health and effective treatment of common problems of the eyes, ears, skin, nervous system and reproductive organs.
1500 POST RD., Darien, CT 06820
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Other Identifiers 8

Other0697273Us Healthcare
Other061258283Chp
Other4111798Aetna
Medicare UPINB83403
Other061258283Guardian
Medicare PIN110009053
Other237210Connecticare
Medicare ID-Type Unspecified110006654

Medicare Participation & PECOS CMS

Medicare enrollment, assignment, and ordering and referring status from the CMS PECOS system.

Medicare Enrollment Status

✔

Enrolled in Medicare and accepts Medicare assignment

Dr. William James Giesen M.d. is registered in PECOS and agrees to accept the Medicare-approved amount as full payment. Medicare patients are not billed beyond the standard deductible and coinsurance.

PECOS PAC ID2567367584
PECOS Enrollment IDI20031203000549
Eligible to Order & Refer✔ Part B Labs & Imaging✔ Durable Medical Equipment✔ Home Health Agency✔ Power Mobility DevicesPer the CMS Ordering and Referring file. Eligibility means Medicare pays claims that this provider orders or refers for these categories.

CLIA Laboratory Certificates CMS CLIA

Laboratory certificates issued under the Clinical Laboratory Improvement Amendments (CLIA) program, which sets federal quality standards for human laboratory testing in the United States. There is no official CMS crosswalk between CLIA and NPI numbers; these certificates are associated with this NPI by matching facility names, locations and phone numbers in the CMS CLIA registry.

Certificate of Waiver 07D0716667

William Giesen MD · Darien, CT
Active · expires Sep 9, 2026
CLIA Number07D0716667
Laboratory TypePhysician Office
Certificate Effective DateSeptember 10, 2024
Certificate Expiration DateSeptember 9, 2026
Laboratory DirectorWilliam J. Giesen
Laboratory Phone(203) 655-2516
Laboratory LocationWilliam Giesen MD1500 Post Road, Darien, CT 06820
CLIA data matches this NPI record on: Address Name Phone
This certificate is issued to a laboratory to perform only waived tests.

Areas of Expertise CMS Part B claims 10

Services this provider delivered to Medicare fee-for-service patients, from the CMS Medicare utilization data. Higher counts generally reflect more experience with a service; care delivered outside Medicare is not included.

Established patient office or other outpatient visit with low level od decision making, if using time, 20 minutes or more 99213
This is a routine visit for patients who have already been seen by the healthcare provider. During this approximately 20-29 minute appointment, your health status will be evaluated and any necessary treatments or tests will be discussed. It's a chance to address any health concerns you may have.
186 services75 patients
Insertion of needle into vein for collection of blood sample 36415
This procedure involves inserting a small needle into a vein, typically in your arm, to collect a blood sample. It's a quick and simple process to help diagnose or monitor health conditions. You may feel a small prick, but discomfort is minimal.
153 services113 patients
Urinalysis, manual test 81002
A urinalysis is a simple, non-invasive test that checks the urine for various elements such as sugar, protein, and signs of infection. It can help detect many common conditions, including kidney disease and diabetes. The manual test involves a lab technician examining a urine sample.
114 services105 patients
Routine electrocardiogram (ecg) using at least 12 leads with interpretation and report 93000
An electrocardiogram (ECG) is a non-invasive test that records your heart's electrical activity. Using 12 leads attached to your body, it captures data to help identify heart conditions. A doctor interprets the results and provides a report.
107 services98 patients
Test to measure expiratory airflow and volume 94010
This test, known as spirometry, assesses how well your lungs work. It measures how much air you can inhale, how much you can exhale and how quickly you can exhale. It's non-invasive and helps diagnose conditions like asthma or COPD.
99 services99 patients
Established patient office or other outpatient visit with moderate level of decision making, if using time, 30 minutes or more 99214
This is a routine check-up for patients who have previously visited our clinic. It involves a comprehensive review of your health and any ongoing treatments. The consultation lasts between 30-39 minutes, allowing enough time to discuss any concerns.
97 services58 patients

Physician Visit Costs CMS claims · ZIP area

Typical Medicare office-visit costs in the 06820 ZIP code area, from fee-for-service claims. These are area statistics, not this provider’s prices; actual charges vary by service and coverage.

New Patient
$138.84 typical visit price
range $60.82 – $183.10
Typical copayment $34.71 (range $15.20 – $45.77)
Most-billed visit code 99204
Established Patient
$106.68 typical visit price
range $19.76 – $149.26
Typical copayment $26.67 (range $4.94 – $37.31)
Most-billed visit code 99214
Amounts reflect what Medicare beneficiaries in this ZIP area are typically charged for office visits. Patients with other coverage should check their individual plans.

Frequently Asked Questions NPPES & CMS

Common questions about this NPI record, answered from the official NPPES registry and CMS datasets shown on this page.

What is William Giesen's NPI number?

The NPI number for William Giesen is 1124104724. It was assigned to this individual provider in the NPPES registry on October 27, 2006.

Where is William Giesen located?

William Giesen practices at 1500 Post Rd., Darien, CT 06820. The listed phone number is (203) 655-2516.

What is William Giesen's specialty?

The primary specialty registered for this NPI is Internal Medicine with taxonomy code 207R00000X.

Is William Giesen enrolled in Medicare?

Yes. William Giesen is registered in the Medicare PECOS system and accepts Medicare assignment, which means accepting the Medicare-approved amount as payment in full for covered services.

Does William Giesen hold a CLIA laboratory certificate?

Yes. A Certificate of Waiver (number 07D0716667) is associated with this NPI, valid through September 9, 2026. CLIA certificates authorize laboratory testing under the federal Clinical Laboratory Improvement Amendments program.

When was this NPI record last updated?

The NPPES record for William Giesen was last updated on May 9, 2016. NPI Profile syncs weekly with the NPPES registry data releases published by CMS. This NPI record was last updated 10 years ago. If this record has changed at CMS more recently, you can request an on-demand re-check against the live CMS registry, directly from this page.