Quick answers
- Which hospitals does Mark J. O'Connor work at?
- Medicare's official clinician data lists Mark J. O'Connor at 3 hospitals: UMass Memorial Health - Harrington Hospital, UMass Memorial Healthalliance Hospitals and UMass Memorial Medical Center/University Campus. This is where the clinician works or has privileges; call the hospital to confirm.
- Where does Mark J. O'Connor see patients?
- Medicare's clinician data lists 2 practice locations, including Leominster, MA and Worcester, MA. Call before your visit to confirm the address.
- What is Mark J. O'Connor's specialty?
- Medicare lists Endocrinology as the primary specialty, and also Internal Medicine.
- Does Mark J. O'Connor accept Medicare assignment?
- Yes. Medicare's clinician data says Mark J. O'Connor 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.
- Does Mark J. O'Connor offer telehealth?
- Medicare's clinician data says Mark J. O'Connor offers telehealth services. Ask the office which visits can be done by video or phone.
- What is the phone number for Mark J. O'Connor?
- (978) 466-4220, as listed in official Medicare / NPI Registry data.
- What is Mark J. O'Connor's NPI number?
- 1518300284. The NPI (National Provider Identifier) is the clinician's permanent federal ID; you can look it up in the official NPI Registry.
Hospitals where Mark J. O'Connor works
Medicare's Facility Affiliation Data lists Mark J. O'Connor at these hospitals (updated 2026-10-02). Each hospital page shows its address, phone, emergency services, Medicare rating and all its clinicians.
- UMass Memorial Health - Harrington HospitalSouthbridge, MA · Acute Care Hospital · CCN 220019
- UMass Memorial Healthalliance HospitalsLeominster, MA · Acute Care Hospital · CCN 220001
- UMass Memorial Medical Center/University CampusWorcester, MA · Acute Care Hospital · CCN 220163
Practice locations
Addresses where Mark J. O'Connor is enrolled with Medicare (CMS data updated 2026-10-02).
- 100 Hospital RdLeominster, MA 01453 (978) 466‑4220
- 55 Lake Ave NWorcester, MA 01655 (508) 334‑1000
Group practices
Medicare enrollment lists Mark J. O'Connor as a member of this group (CMS data updated 2026-10-02).
- UMass Memorial Medical Group Inc2,516 clinicians in the group
Specialties
- Endocrinologyprimary
- Internal Medicinealso
Other endocrinologists 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 | 2013 |
| Gender (as listed) | Male |
| Medicare assignment | Accepts (Medicare-approved amount as full payment) |
| Telehealth | Offers telehealth services |
| NPI (National Provider Identifier) | 1518300284 |
| 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