NPI Portal NPI Lookup & Verification

Type 1 · Individual ✓ Active NPI ✓ Valid NPI checksum

Dr. William Edward Callahan Jr., MD

Psychiatry Physician in Aliso Viejo, CA · enumerated 2006 · practices at Anthony M. Kassir, M.D., A Professional Medical Corporation.

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

National Provider Identifier

1538130513

Verified

See something wrong? Report a correction

Registry record

Entity type Individual (Type 1)
Name Dr. William Edward Callahan Jr.
Credential MD
Sex Male
Practice address 120 Vantis, Suite 540, Aliso Viejo, CA, 92656
Phone (949) 916-5656
Fax (949) 916-5657
Enumeration date Jan 30, 2006
Last updated in NPPES Jul 8, 2007

Taxonomy & licenses

2084P0800X Psychiatry Physician Allopathic & Osteopathic Physicians · License G62750 (CA) 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

Where does William Callahan practice?
The practice location on file with NPPES is in Aliso Viejo, CA. Providers can have multiple locations; NPPES lists the primary practice address.
What is the NPI number for William Callahan?
The National Provider Identifier (NPI) for William Callahan is 1538130513, a Type 1 (individual) record in the CMS NPPES registry.

Other providers at this practice address

Browse all →

Source: CMS NPPES (public data). Snapshot 2026-07-13. Provider record last updated 2007-07-08.