Provider records sourced from NPPES (CMS National Plan & Provider Enumeration System). Data current as of August 10, 2026.
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Dr. William James Giesen, MD

Individual provider Internal Medicine Physician · NPI 1124104724

Dr. William James Giesen, MD is an Internal Medicine in Darien, Connecticut. Graduated from Georgetown University School of Medicine in 1975, 51 years ago. Practices as a sole proprietor and accepts Medicare assignment. Licensed in Connecticut.

Years since qualifying
51
Trained at
Georgetown University School of Medicine
Licensed in
CT
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

1500 Post Rd
Darien, CT 06820
Phone: (203) 655-2516
Fax: (203) 656-3665
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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 CT023721 (CT)

Record details

NPI number1124104724
Entity typeIndividual (Type 1)
GenderMale
Credentials MD
Sole proprietorYes
NPI enumeratedOctober 27, 2006
Last updated in NPPESMay 9, 2016

Medicare enrollment

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

Medicare specialtyINTERNAL MEDICINE
Medical schoolGEORGETOWN UNIVERSITY SCHOOL OF MEDICINE
Graduated 1975 (51 years in practice)
Accepts Medicare assignment Yes — accepts the Medicare-approved amount

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