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

Dr. Mark Jacob Siedner, MD

Individual provider Infectious Disease Physician · NPI 1548429178

Dr. Mark Jacob Siedner, MD is registered under Infectious Disease in Boston, Massachusetts. Graduated from Johns Hopkins University School of Medicine in 2007, 19 years ago. Practices with Massachusetts General Physicians Organization Inc, a 3,484-clinician group and accepts Medicare assignment. Licensed in Massachusetts.

Years since qualifying
19
Trained at
Johns Hopkins University School of Medicine
Licensed in
MA
In the registry since
2008
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

55 Fruit St Massachusetts General Hospital GRJ504
Boston, MA 02114-2621 Not confirmed with CMS for 13 years — call before visiting
Phone: (617) 726-3812
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Pin is approximate — placed at the ZIP-code centre, not the exact door.

Specialties & licences

Infectious Disease Physician (primary) Taxonomy 207RI0200X · Licence 253779 (MA)

Record details

NPI number1548429178
Entity typeIndividual (Type 1)
GenderMale
Credentials MD
Sole proprietorNo
NPI enumeratedJune 9, 2008
Last updated in NPPESDecember 8, 2012

Medicare enrollment

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

Medicare specialtyINFECTIOUS DISEASE
Also practisesINTERNAL MEDICINE
Medical schoolJOHNS HOPKINS UNIVERSITY SCHOOL OF MEDICINE
Graduated 2007 (19 years in practice)
Group practice Massachusetts General Physicians Organization Inc — 3484 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 patients59
Services billed 178 a service is one billed item, such as a visit, a test or a procedure
Average patient age72

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.

Practises at

Facilities the CMS Facility Affiliation file lists for this clinician.

Colleagues at Massachusetts General Physicians Organization Inc

Clinicians the CMS Doctors & Clinicians file lists under the same group practice. CMS counts 3484 clinicians in the practice; 12 are shown here.

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