Type 1 · Individual ✓ Active NPI ✓ Valid NPI checksum Sole proprietor

Dr. William James Giesen, M.D.

Internal Medicine Physician in Darien, CT · enumerated 2006 · practices at Robert A. Lindberg, MD, LLC.

Data current as of Jul 13, 2026 · sourced from CMS NPPES

National Provider Identifier

1124104724

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Registry record

Entity type Individual (Type 1)

Name Dr. William James Giesen

Credential M.D.

Sex Male

Practice address Darien, CT, 06820

Phone (203) 655-2516

Fax (203) 656-3665

Enumeration date Oct 27, 2006

Last updated in NPPES May 9, 2016

Street address withheld: NPPES sole-proprietor addresses can be home addresses. See our data policy.

Taxonomy & licenses

207R00000X Internal Medicine Physician Allopathic & Osteopathic Physicians · License CT023721 (CT) Primary

MD · Doctor of Medicine: A physician who completed medical school (allopathic medicine), residency training, and state licensure. About the MD credential

Other identifiers

Identifier	Type	State	Issuer
061258283	Other	-	GUARDIAN
0697273	Other	-	US HEALTHCARE
4111798	Other	-	AETNA
061258283	Other	-	CHP
237210	Other	-	CONNECTICARE

What is an NPI number?

A National Provider Identifier (NPI) is a unique 10-digit number that CMS assigns to every U.S. healthcare provider and organization under HIPAA. Type 1 NPIs identify individual providers; Type 2 NPIs identify organizations. The NPI appears on insurance claims, prescriptions, and credentialing paperwork, and never changes, even if the provider moves or changes specialty.

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Frequently asked questions

How do I verify William Giesen's NPI record?

Cross-check NPI 1124104724 against the official CMS registry at npiregistry.cms.hhs.gov. This page mirrors the same public NPPES data with a monthly snapshot.

Is NPI 1124104724 active?

Yes, as of the latest NPPES snapshot, NPI 1124104724 is active (record last updated 2016-05-09).

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Source: CMS NPPES (public data). Snapshot 2026-07-13. Provider record last updated 2016-05-09.