Katharine Willoughby, MD
Obstetrics & Gynecology Physician · Stanford, CA
Katharine Willoughby, MD is an obstetrics & gynecology physician with a practice address in Stanford, California, and NPI 1053643684, issued on Feb 7, 2010. Check the license (California A110248, as entered in NPPES) on the Medical Board of California; the Medicare figures below come from public CMS files.
- Name
- Katharine Willoughby
- Credential
- MD
- Primary taxonomy
- Obstetrics & Gynecology Physician 207V00000X
- License number
- A110248 CA
Self-reported in NPPES; status is on the state search - Practice location
- 300 Pasteur Dr, Stanford, CA 94305
- Phone
- (650) 723-6661
- Enumerated
- Feb 7, 2010
- Record last updated
- Dec 15, 2021 (not updated in 5 years: call before relying on the address or phone)
- Medicare enrollment
- Enrolled (PECOS I20121030000477); accepts Medicare assignment
- Medical or professional school
- University Of California, Davis School Of Medicine, 2008
- Entity
- Type 1 · individual
8 nearest obstetrics & gynecology physician records → All 5,088 in California → Look up another NPI →
Also registered at 300 Pasteur Dr
A shared address usually means a shared clinic or building; it does not show who employs whom.
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Verify Katharine Willoughby in five checks
- 1IdentityNPI record in CMS NPPESNPI lookupConfirmed in NPPES
- 2LicenseActive license and public ordersMedical Board of California
Search for license A110248Check the board - 3Other statesLicenses and actions elsewhereDocInfo (FSMB)Not checked
- 4ExclusionsMedicare and Medicaid bansHHS-OIG exclusion listNot checked
- 5CertificationBoard certificationABMS AOA NCCPA AANPNot checked
18% fewer Medicare Part D claims than the average obstetrics & gynecology physician in 2024
135 Medicare Part D claims for 90 beneficiaries, against an average of 165 among the 28,733 providers of this specialty who prescribed in Part D. Brand-name drugs were 18% of claims.
Most prescribed
- Estradiol42 claims
- Trospium Chloride13 claims
Source: CMS Medicare Part D Prescribers by Provider and Drug, 2024 (data.cms.gov). Part D covers prescriptions for Medicare patients only; drugs with fewer than 11 claims are not published.
Bills Medicare through one group practice
- Permanente Medical Group IncSanta Clara, CA
Source: CMS Doctors and Clinicians National Downloadable File (the group practices a clinician bills Medicare through) (data.cms.gov).
Katharine Willoughby among 5,088 obstetrics & gynecology physician records in California
Katharine Willoughby, MD is one of 5,088 obstetrics & gynecology physician records with a practice address in California. 74% of them appear in a Medicare file (Part D prescribing, MIPS, Open Payments or Medicare group billing); this one does. Its NPI, issued in 2010, is newer than 70% of them.
- NPI issued2010 · 70% of these records are older, 28% newer
- In a Medicare fileYes · 74% of these records are
- In the CMS Doctors and Clinicians fileYes · 53% of these records are
- Graduated2008 · median 2004 among the 2,700 with a school on file
- Record last updated2021 · 64% of these records were not updated in five years or more
Source: CMS NPPES, file of Aug 9, 2026, every record with primary taxonomy 207V00000X and a California practice address; Medicare files: CMS Part D Prescribers 2024, MIPS 2023, Open Payments 2024, Doctors and Clinicians (data.cms.gov).
Obstetrics & Gynecology Physician providers in California
There are 5,088 obstetrics & gynecology physician records in California.
All 5,088 in California → Every provider in Stanford → Obstetrics & Gynecology Physician nationwide →
The 8 obstetrics & gynecology physician records with the nearest ZIP codes
- Anna Altshuler, MDStanford, CA 943051447583877
- Rachel Chan Seay, MDStanford, CA 943051578790127
- Brooke Friedman, M.D.Stanford, CA 943051487836052
- Amreen Husain, MDStanford, CA 943051790856474
- Mary JacobsonStanford, CA 943051952443913
- Michelle Khan, MDStanford, CA 943051699970947
- Jonathan Kort, M.D.Stanford, CA 943051326364332
- Lisa Lee, MDStanford, CA 943051952374936
Common questions
What is Katharine Willoughby, MD's NPI number?
Katharine Willoughby, MD's National Provider Identifier (NPI) is 1053643684, issued on Feb 7, 2010. An NPI identifies a provider in billing; it is not a license.
Where is Katharine Willoughby, MD located?
The NPPES record lists a practice address at 300 Pasteur Dr, Stanford, CA, 94305. Phone: (650) 723-6661. Providers update this record themselves, so call before visiting.
How can I verify Katharine Willoughby, MD's license?
NPPES lists California license number A110248, as entered by the provider. Search the Medical Board of California at https://www.mbc.ca.gov/License-Verification/default.aspx. The NPPES record confirms identity only; the state search shows license status, expiration and public orders.
How much does Katharine Willoughby, MD prescribe under Medicare Part D?
In 2024, Katharine Willoughby, MD had 135 Medicare Part D claims for 90 beneficiaries; the average among obstetrics & gynecology physician prescribers was 165. Part D covers Medicare prescriptions only.
Source: CMS National Plan and Provider Enumeration System (NPPES), file of Aug 9, 2026 (NPPES files on CMS.gov); NUCC Health Care Provider Taxonomy. Medicare files from data.cms.gov. An NPI identifies who bills; it is not a license.
Figures on PlainDoctor are read from the federal files each page names (CMS NPPES, Medicare Part D, MIPS, Open Payments; the HHS-OIG exclusion list only as counts) and from Census population estimates, with the file date shown beside them. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of Aug 9, 2026.