Provider records sourced from NPPES (CMS National Plan & Provider Enumeration System). Data current as of October 4, 2026.
NPIDirectory

Mark C Johnson, MD

Individual provider Internal Medicine Physician · NPI 1013923127

Mark C Johnson, MD practises Endocrinology in Mason City, Iowa. Graduated from University of Iowa, Rj & L Carver College of Medicine in 1977, 49 years ago. Practices with North Iowa Mercy Clinics, a 300-clinician group and accepts Medicare assignment. Licensed in Iowa.

Years since qualifying
49
Trained at
University of Iowa, Rj & L Carver College of Medicine
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

910 N Eisenhower Ave
Mason City, IA 50401-2800
Phone: (641) 428-7799
Fax: (641) 428-5274
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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 21527 (IA)

Record details

NPI number1013923127
Entity typeIndividual (Type 1)
GenderMale
Credentials MD
Sole proprietorNo
NPI enumeratedJuly 31, 2006
Last updated in NPPESJuly 8, 2025
Certification dateJuly 8, 2025

Medicare enrollment

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

Medicare specialtyENDOCRINOLOGY
Also practisesINTERNAL MEDICINE
Medical schoolUNIVERSITY OF IOWA, RJ & L CARVER COLLEGE OF MEDICINE
Graduated 1977 (49 years in practice)
Group practice North Iowa Mercy Clinics — 300 clinicians
Accepts Medicare assignment Yes — accepts the Medicare-approved amount

Medicare patients and services, 2024

From the CMS Medicare Physician & Other Practitioners file for calendar year 2024. It counts Original Medicare patients only, so a practice that mostly sees Medicare Advantage or privately insured patients looks smaller here than it is.

Medicare patients1,561
Services billed 3,877 a service is one billed item, such as a visit, a test or a procedure
Average patient age77

Dollar amounts are not shown. What Medicare pays a practice is gross billings, before staff, premises and tax and including the cost of any drugs it administers, so it is not what a clinician earns.

Payments from drug and device companies, 2025

Drug and device makers are required by federal law (the Physician Payments Sunshine Act) to report what they pay or give to clinicians, and CMS publishes the reports as Open Payments. This is the 2025 program year. A report is a record of a payment, not an allegation of anything, and many are small items such as meals. Only general payments are listed here; research payments and ownership or investment interests are reported separately by CMS and are not shown.

Compensation for services other than consulting , including serving as faculty or as a speaker at a venue other than a continuing education program $25,343 11 payments
Travel and Lodging $1,893 9 payments · travel or lodging paid or reimbursed, such as to attend a conference
Food and Beverage $962 15 payments · a meal or drink at a meeting or visit, not a fee

Each amount is the sum of what companies reported for that kind of payment in 2025, rounded to the dollar. Not all of it is income to the clinician: a meal is not a fee, a charitable contribution goes to a charity, and a royalty or an acquisition payment is not a salary.

Check a report, or dispute one, at the source in CMS’s own tool, Open Payments. Corrections go through CMS’s dispute process. This site removes a home address on request and asks for no proof, because that is privacy; it will not remove an accurate payment report on request, because that is a statutory public disclosure.

Practises at

Facilities the CMS Facility Affiliation file lists for this clinician. Those with a page here are linked.

Colleagues at North Iowa Mercy Clinics

Clinicians the CMS Doctors & Clinicians file lists under the same group practice. CMS counts 300 clinicians in the practice; 12 are shown here.

Other providers in Mason City