William James Giesen, M.D.
NPI 1124104724ActiveIndividual· Internal Medicine· Darien, CT
Internal Medicine (M.D.) in Darien, Connecticut, trained at Georgetown University School of Medicine (class of 1975). 140 Medicare patients in 2024, $44,631 paid; nearly all of their 1,595 Part D prescriptions were generic (91%). Abbvie Inc. reported $28.57 in payments in 2025, mostly food and beverage.
Overview
| NPI | 1124104724 |
|---|---|
| Status | Active |
| Entity type | Individual |
| Credential | M.D. |
| Sole proprietor | Yes |
| NPI issued | Oct 27, 2006 |
| Last updated in NPPES | May 9, 2016 |
Specialties and licenses
| Taxonomy | Code | License | State |
|---|---|---|---|
| Internal Medicine Primary | 207R00000X | CT023721 | CT |
Exclusion screening
| List | Result | Details |
|---|---|---|
| HHS-OIG LEIE · Nov 10, 2026 | No match | Checked by NPI and by name + state |
| North Carolina Medicaid · Nov 11, 2026 | No match | — |
| New York OMIG · Nov 11, 2026 | No match | — |
| Ohio Medicaid · Nov 11, 2026 | No match | — |
| Pennsylvania Medicheck · Nov 11, 2026 | No match | — |
| Washington HCA · Nov 11, 2026 | No match | — |
Official OIG search · How matching works ·Bulk check a roster
Medicare
| Enrollment (PECOS) | Enrolled Practitioner - Internal Medicine (CT) |
|---|---|
| Accepts assignment | Yes (participating) |
Medicare services in 2024
| Medicare patients | 140 |
|---|---|
| Services billed | 915 across 17 procedure codes |
| Paid by Medicare | $44,631 |
Part D prescriptions in 2024
| Prescriptions (claims) | 1,595 · 3,104 30-day fills |
|---|---|
| Patients | 165 |
| Total drug cost | $65,080 |
| Generic share | 91% of claims |
Education and affiliations
| Medical school | Georgetown University School of Medicine |
|---|---|
| Graduation year | 1975 |
| Medicare specialty | Internal Medicine |
Hospital affiliations
- Greenwich Hospital Association -Greenwich, CT
- Stamford HospitalStamford, CT
Industry payments (Open Payments)
- 2025$28.57 · 1 payment from 1 company
Top paying companies in 2025
| Company | Amount | Payments |
|---|---|---|
| Abbvie Inc. | $28.57 | 1 |
What the 2025 payments were for
- Food and Beverage$28.57 · 1 payment
Receiving payments does not imply wrongdoing. What Open Payments covers ·original records
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All 19 internal medicine physicians in Darien · All internal medicine physicians in Connecticut