DR. MARK E WILLIAMS MD
NPI 1184653891
Internal Medicine - Nephrology in Boston, MA
About Dr. Mark E Williams Md NPPES
Official registry information on file with the National Plan and Provider Enumeration System.
DR. MARK E WILLIAMS MD (NPI 1184653891) is an individual nephrology provider in Boston, Massachusetts, licensed in Massachusetts (45103) and active in the NPI registry since July 2006. He is enrolled in Medicare PECOS and is a graduate of Indiana University School Of Medicine (1977).
NPPES Registry Identity
Specialties & Licenses 2
Other Identifiers 3
Accepted Insurance
Medicare Participation & PECOS CMS
Medicare enrollment, assignment, billing reassignment, and ordering and referring status from CMS.
Medicare Enrollment Status
Enrolled in Medicare and accepts Medicare assignment
Dr. Mark E Williams Md 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.
Medicare Billing Reassignments
5Medicare enrollment records show Mark Williams reassigns Medicare billing to 5 organizations. Each organization bills Medicare for the services this provider delivers there; the nearest is listed first.
Boston, MA 02215
- Reassigned Medicare billing, Massachusetts enrollment
- 125 clinicians in this Medicare group
Boston, MA 02215
- Reassigned Medicare billing, Massachusetts enrollment
- 1,477 clinicians in this Medicare group
Boston, MA 02215
- Reassigned Medicare billing, Massachusetts enrollment
- 2,579 clinicians in this Medicare group
Los Angeles, CA 90033
- Reassigned Medicare billing, California enrollment
- 2,445 clinicians in this Medicare group
Los Angeles, CA 90033
- Reassigned Medicare billing, California enrollment
- 24 clinicians in this Medicare group
Source: CMS Revalidation Reassignment List, October 2026 release. Reassignment records can lag staffing changes; confirm a current affiliation with the organization.
Areas of Expertise CMS Part B claims 9
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.
Physician Visit Costs CMS claims · ZIP area
Typical Medicare office-visit costs in the 02215 ZIP code area, from fee-for-service claims. These are area statistics, not this provider’s prices; actual charges vary by service and coverage.
Referred Medical Equipment & Supplies CMS DME claims 4
Durable medical equipment, devices and supplies this provider ordered from DME suppliers for patients, from Medicare fee-for-service claims.
Other Providers at the Same Location NPPES 20
Providers registered at the same practice address, or within the immediate area, according to the NPPES registry.
BOSTON, MA 02215
BOSTON, MA 02215
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 Mark Williams's NPI number?
The NPI number for Mark Williams is 1184653891. It was assigned to this individual provider in the NPPES registry on July 3, 2006.
Where is Mark Williams located?
Mark Williams practices at 1 Joslin Pl, Boston, MA 02215. The listed phone number is (617) 732-2477.
What is Mark Williams's specialty?
The primary specialty registered for this NPI is Internal Medicine, specializing in Nephrology, with taxonomy code 207RN0300X.
Is Mark Williams enrolled in Medicare?
Yes. Mark Williams 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.
Which organizations bill Medicare for Mark Williams's services?
According to the CMS Revalidation Reassignment List (October 2026 release), Mark Williams reassigns Medicare benefits to 5 organizations: Joslin Clinic Inc (Boston, MA), Beth Israel Deaconess Medical Center, Inc. (Boston, MA), Harvard Medical Faculty Phys At Beth Israel Deaconess Med Ctr Inc (Boston, MA), Usc Care Medical Group, Inc (Los Angeles, CA) and Usc Care Medical Non-Contracted LLC (Los Angeles, CA). Each reassignment is filed with Medicare on form CMS-855R, signed by both the clinician and the organization, and lets the organization bill Medicare and receive payment for Mark Williams's services. Reassignment records can lag staffing changes; confirm current arrangements with the organization.
What insurance does Mark Williams accept?
Health plans from Taro Health list Mark Williams as in-network in at least one marketplace plan. Coverage varies by plan and year; verify with the insurer or the provider before a visit.
When was this NPI record last updated?
The NPPES record for Mark Williams was last updated on April 25, 2011. NPI Profile syncs weekly with the NPPES registry data releases published by CMS. This NPI record was last updated 15 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.
# Dr. Mark E Williams, MD · NPI 1184653891
Nephrology physician in Boston, Massachusetts. Individual provider, active in the CMS NPPES registry since July 3, 2006.
## Identity
- **NPI:** 1184653891 (Entity type: Individual)
- **Enumerated:** July 3, 2006
- **Primary specialty:** Internal Medicine - Nephrology · taxonomy 207RN0300X
- **State license:** 45103 (Massachusetts)
- **Sole proprietor:** No
## Practice location
- **Address:** 1 JOSLIN PL, Boston, MA 02215-5306
- **Phone:** (617) 732-2477 · **Fax:** (617) 732-2467
## Medicare
- **Medicare:** Enrolled (PECOS); accepts Medicare assignment
- **Ordering & referring:** eligible for Part B labs & imaging, durable medical equipment, home health, power mobility devices
- **Bills Medicare through:** 5 organizations under Medicare reassignment (form CMS-855R): Joslin Clinic Inc (NPI 1528003621, Boston, MA); Beth Israel Deaconess Medical Center, Inc. (NPI 1548202641, Boston, MA); Harvard Medical Faculty Phys At Beth Israel Deaconess Med Ctr Inc (NPI 1194765438, Boston, MA); Usc Care Medical Group, Inc (NPI 1902846306, Los Angeles, CA); Usc Care Medical Non-Contracted LLC (NPI 1659509206, Los Angeles, CA) · CMS Revalidation Reassignment List, October 2026 release
- **Medical school:** Indiana University School Of Medicine, class of 1977
## Record status
- **NPPES last updated:** April 25, 2011
- **Other identifiers:** Medicare ID-Type Unspecified E05276; Medicare UPIN C46385 (MA); Medicaid 0112542 (MA)
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Source: [NPI Profile](https://npiprofile.com/npi/1184653891) · Data from the CMS NPPES public registry.