Quick answers
- Which hospitals does William J. Riesen work at?
- Medicare's official clinician data lists William J. Riesen at 4 hospitals: Franklin General Hospital, Iowa Specialty Hospital - Belmond, MercyOne Des Moines Medical Center and MercyOne North Iowa Medical Center. This is where the clinician works or has privileges; call the hospital to confirm.
- Where does William J. Riesen see patients?
- Medicare's clinician data lists 3 practice locations, including Mason City, IA and New Hampton, IA. Call before your visit to confirm the address.
- What is William J. Riesen's specialty?
- Medicare lists Internal Medicine as the primary specialty.
- Does William J. Riesen accept Medicare assignment?
- Yes. Medicare's clinician data says William J. Riesen 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 J. Riesen?
- (641) 428-7847, as listed in official Medicare / NPI Registry data.
- What is William J. Riesen's NPI number?
- 1548377997. 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 J. Riesen works
Medicare's Facility Affiliation Data lists William J. Riesen at these hospitals (updated 2026-10-02). Each hospital page shows its address, phone, emergency services, Medicare rating and all its clinicians.
- Franklin General HospitalHampton, IA · Critical Access Hospital · CCN 161308
- Iowa Specialty Hospital - BelmondBelmond, IA · Critical Access Hospital · CCN 161301
- MercyOne Des Moines Medical CenterDes Moines, IA · Acute Care Hospital · CCN 160083
- MercyOne North Iowa Medical CenterMason City, IA · Acute Care Hospital · CCN 160064
Practice locations
Addresses where William J. Riesen is enrolled with Medicare (CMS data updated 2026-10-02).
- 1000 4th St SWMason City, IA 50401
- 1010 4th St SW, 105 Mercyone North Iowa Neurosurgery CareMason City, IA 50401 (641) 428‑7847
- 308 N Maple Ave, Mercyone New Hampton Medical CenterNew Hampton, IA 50659 (641) 394‑4121
Group practices
Medicare enrollment lists William J. Riesen as a member of this group (CMS data updated 2026-10-02).
- North Iowa Mercy Clinics302 clinicians in the group
Specialties
- Internal Medicineprimary
Other internal medicine doctors in Mason City
Clinicians with the same Medicare primary specialty in Mason City, IA — not a recommendation.
Clinician information
| Credential | MD |
|---|---|
| Medical school | Perelman School Of Med At The University Of Pennsylvania |
| Graduation year | 1993 |
| Gender (as listed) | Male |
| Medicare assignment | Accepts (Medicare-approved amount as full payment) |
| NPI (National Provider Identifier) | 1548377997 |
| 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