Provider records sourced from NPPES (CMS National Plan & Provider Enumeration System). Data current as of August 10, 2026.
NPIDirectory

Dr. William J Riesen, MD

Individual provider Internal Medicine Physician · NPI 1548377997

Dr. William J Riesen, MD is an Internal Medicine in Mason City, Iowa. Graduated from Perelman School of Med at the University of Pennsylvania in 1993, 33 years ago. Practices with North Iowa Mercy Clinics, a 300-clinician group and accepts Medicare assignment. Licensed in Iowa.

Years since qualifying
33
Trained at
Perelman School of Med at the University of Pennsylvania
Licensed in
IA
In the registry since
2006
What do these letters mean?
MD — Doctor of Medicine
A physician who completed allopathic medical school.

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Practice location Address checks out

1010 4th St SW Ste 305
Mason City, IA 50401-2801
Phone: (641) 428-5700
Fax: (641) 428-2515
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Pin is approximate — placed at the ZIP-code centre, not the exact door.

Specialties & licences

Internal Medicine Physician (primary) Taxonomy 207R00000X · Licence 31260 (IA)

Record details

NPI number1548377997
Entity typeIndividual (Type 1)
GenderMale
Credentials MD
Sole proprietorNo
NPI enumeratedAugust 23, 2006
Last updated in NPPESJuly 14, 2025
Certification dateJuly 14, 2025
Mailing address621 S Illinois Ave, Suite 103, Mason City, IA 50401-5489

Medicare enrollment

From the CMS Doctors & Clinicians file — this clinician is enrolled in Medicare.

Medicare specialtyINTERNAL MEDICINE
Medical schoolPERELMAN SCHOOL OF MED AT THE UNIVERSITY OF PENNSYLVANIA
Graduated 1993 (33 years in practice)
Group practice North Iowa Mercy Clinics — 300 clinicians
Accepts Medicare assignment Yes — accepts the Medicare-approved amount
Practice locations2 on file with Medicare

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