John Williams, M.D.
NPI 1265516421 · Gastroenterology Physician · Madison, WI
Enrolled with Medicare as Practitioner - Gastroenterology · source: CMS PECOS Public Provider Enrollment (2026.04.01)
John Williams, M.D. is a Gastroenterology Physician provider in Madison, WI (NPI 1265516421).
Provider details
- NPI number
- 1265516421
- Entity type
- Individual
- Primary specialty
- Gastroenterology PhysicianAllopathic & Osteopathic Physicians
- Credential
- M.D.
- Sex
- Male
- Sole proprietor
- No
- License
- 43694-020 (WI)
Specialties & taxonomies
Allopathic & Osteopathic Physicians
Profile Score
A profile completeness & documented-activity index — NOT a quality, outcomes, or patient-satisfaction rating.
- Registry tenure28% of score
19 yrs in NPPES registry
- Profile completeness28% of score
100% of core fields populated
- Practice footprint17% of score
1 documented practice location
- Medicare service volume (vs. specialty peers)28% of score
470 Medicare services, 2024 (ranked within specialty)
Medicare volume is ranked against active providers in the same specialty. Signals a provider has no public data for (e.g. Medicare claims) are left out of the score entirely — never counted as zero — so providers without that data are not penalized. See the full formula and weights in our methodology.
What this provider does (Medicare)
Based on Medicare fee-for-service claims, 2024; not all care is captured.
| Service (HCPCS) | Medicare services | Typical Medicare-allowed (2024) |
|---|---|---|
| Biopsy of Esophagus, Stomach, And/Or Upper Small Bowel Using a Flexible Endoscope43239 | 63 | $93 |
| Biopsy of Large Bowel Using a Flexible Endoscope45380 | 55 | $152 |
| Biopsy of Large Bowel Using a Flexible Endoscope45380 | 50 | $116 |
| Removal of Polyps Or Growths of Large Bowel Using an Endoscope With Mechanical Snare45385 | 42 | $229 |
| Removal of Polyps Or Growths of Large Bowel Using an Endoscope With Mechanical Snare45385 | 39 | $219 |
What this provider prescribes (Medicare Part D)
Top drugs by Medicare Part D claim volume, 2024 · 13 distinct drugs on file.
| Drug | Part D claims (2024) | Beneficiaries |
|---|---|---|
| Peg3350/Sod Sulf,bicarb,cl/Kclbrand: Gavilyte-C | 271 | 254 |
| Omeprazole | 70 | 17 |
| Famotidine | 33 | 11 |
| Mesalamine | 29 | — |
| Balsalazide Disodium | 28 | — |
| Adalimumabbrand: Humira(cf) Pen | 25 | — |
| Peg3350/Sod Sulf,bicarb,cl/Kclbrand: Gavilyte-G | 24 |
Practice location
Mailing address
Registry dates
- Enumerated
- 2006-10-24
- Last updated
- 2021-01-27
- Certified
- 2021-01-27
Frequently asked questions
- What is John Williams's NPI number?
- John Williams's National Provider Identifier (NPI) is 1265516421, a unique 10-digit ID issued by CMS for use in standard healthcare transactions.
- What is John Williams's specialty?
- John Williams is listed in the NPPES registry with a primary specialty of Gastroenterology Physician (Allopathic & Osteopathic Physicians).
- Where is John Williams located?
- John Williams's practice location on file with NPPES is 20 S Park St, Madison, WI 53715-1348.
- What is John Williams's phone number?
- The practice phone number listed in the NPPES registry for John Williams is (608) 287-2680.
- Does John Williams accept Medicare?
- John Williams is approved to bill Medicare according to CMS PECOS enrollment data (2026.04.01). Confirm current participation with the provider before scheduling.
- Is John Williams's NPI active?
- Yes — John Williams's NPI (1265516421) is active in the NPPES registry as of the last update on 2021-01-27.
Source: CMS NPPES Data Dissemination (June 2026). NPI Central is not affiliated with CMS. Data is provided as-is from the public registry.