Type 1 · Individual ✓ Active NPI ✓ Valid NPI checksum Sole proprietor

Dr. James John O'Leary, M.D.

Medical Oncology Physician in Waltham, MA · enumerated 2009.

Data current as of Jul 13, 2026 · sourced from CMS NPPES

National Provider Identifier

1336371012

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Registry record

Entity type Individual (Type 1)

Name Dr. James John O'Leary

Credential M.D.

Sex Male

Practice address Waltham, MA, 02451

Phone (781) 895-0600

Fax (781) 895-0611

Enumeration date Aug 14, 2009

Last updated in NPPES Aug 14, 2009

Street address withheld: NPPES sole-proprietor addresses can be home addresses. See our data policy.

Taxonomy & licenses

207RX0202X Medical Oncology Physician Allopathic & Osteopathic Physicians · License 188142 (NY) Primary

MD · Doctor of Medicine: A physician who completed medical school (allopathic medicine), residency training, and state licensure. About the MD credential

What is an NPI number?

A National Provider Identifier (NPI) is a unique 10-digit number that CMS assigns to every U.S. healthcare provider and organization under HIPAA. Type 1 NPIs identify individual providers; Type 2 NPIs identify organizations. The NPI appears on insurance claims, prescriptions, and credentialing paperwork, and never changes, even if the provider moves or changes specialty.

Read the full guide → Validate an NPI →

Frequently asked questions

What is the NPI number for James O'Leary?

The National Provider Identifier (NPI) for James O'Leary is 1336371012, a Type 1 (individual) record in the CMS NPPES registry.

Where does James O'Leary practice?

The practice location on file with NPPES is in Waltham, MA. Providers can have multiple locations; NPPES lists the primary practice address.

Source: CMS NPPES (public data). Snapshot 2026-07-13. Provider record last updated 2009-08-14.