Quick answers
- Which hospitals does William C. O Callahan work at?
- Medicare's official clinician data lists William C. O Callahan at 1 hospital: UMass Memorial Medical Center/University Campus. This is where the clinician works or has privileges; call the hospital to confirm.
- Where does William C. O Callahan see patients?
- Medicare's clinician data lists 2 practice locations, including Wilbraham, MA and Holden, MA. Call before your visit to confirm the address.
- What is William C. O Callahan's specialty?
- Medicare lists Emergency Medicine as the primary specialty.
- Does William C. O Callahan accept Medicare assignment?
- Yes. Medicare's clinician data says William C. O Callahan accepts Medicare assignment (the Medicare-approved amount as full payment for covered services), as of 2026-10-02. Ask the office to confirm before your visit.
- What is the phone number for William C. O Callahan?
- (413) 599-3800, as listed in official Medicare / NPI Registry data.
- What is William C. O Callahan's NPI number?
- 1114964186. The NPI (National Provider Identifier) is the clinician's permanent federal ID; you can look it up in the official NPI Registry.
Hospitals where William C. O Callahan works
Medicare's Facility Affiliation Data lists William C. O Callahan at these hospitals (updated 2026-10-02). Each hospital page shows its address, phone, emergency services, Medicare rating and all its clinicians.
- UMass Memorial Medical Center/University CampusWorcester, MA · Acute Care Hospital · CCN 220163
Practice locations
Addresses where William C. O Callahan is enrolled with Medicare (CMS data updated 2026-10-02).
- 2040 Boston Rd, Suite 5Wilbraham, MA 01095 (413) 599‑3800
- 5 Shrewsbury St, Suite DHolden, MA 01520 (508) 829‑3800
Group practices
Medicare enrollment lists William C. O Callahan as a member of this group (CMS data updated 2026-10-02).
- Urgent Care Specialists PC10 clinicians in the group
Specialties
- Emergency Medicineprimary
Other emergency medicine doctors in Massachusetts
Clinicians with the same Medicare primary specialty in Massachusetts — not a recommendation.
Clinician information
| Credential | MD |
|---|---|
| Medical school | University Of Massachusetts Medical School |
| Graduation year | 1990 |
| Gender (as listed) | Male |
| Medicare assignment | Accepts (Medicare-approved amount as full payment) |
| NPI (National Provider Identifier) | 1114964186 |
| Corrections | Report an error or suggest an update → |
Most corrections must be made at the source: clinicians update their NPI Registry record (NPPES) and their Medicare enrollment (PECOS); this page follows the next data release.
Sources
- Facility Affiliation Data — Centers for Medicare & Medicaid Services (CMS), data updated 2026-10-02, retrieved 2026-10-29
- National Downloadable File (Doctors and Clinicians) — CMS, data updated 2026-10-02, retrieved 2026-10-29
- NPI Registry — U.S. Department of Health and Human Services (NPPES), the clinician’s official record
- Medicare Care Compare — official Medicare tool to look up clinicians