Type 1 · Individual ✓ Active NPI ✓ Valid NPI checksum

Mark T Duffy, MD

Q: What is the NPI number for Mark Duffy?

The National Provider Identifier (NPI) for Mark Duffy is 1235167537, a Type 1 (individual) record in the CMS NPPES registry.

Ophthalmic Plastic and Reconstructive Surgery Physician in Green Bay, WI · enumerated 2006.

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

National Provider Identifier

1235167537

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Registry record

Entity type Individual (Type 1)

Name Mark T Duffy

Credential MD

Sex Male

Practice address 2253 W Mason St, Green Bay, WI, 54303

Phone (920) 327-7000

Fax (920) 327-7005

Enumeration date Jun 28, 2006

Last updated in NPPES Apr 21, 2026

Taxonomy & licenses

207W00000X Ophthalmology Physician Allopathic & Osteopathic Physicians · License 47208 (WI) Secondary

207WX0200X Ophthalmic Plastic and Reconstructive Surgery Physician Allopathic & Osteopathic Physicians · License 47208 (WI) 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
34564300	Medicaid	WI	-

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

Where does Mark Duffy practice?

The practice location on file with NPPES is in Green Bay, WI. Providers can have multiple locations; NPPES lists the primary practice address.

What is the NPI number for Mark Duffy?

The National Provider Identifier (NPI) for Mark Duffy is 1235167537, a Type 1 (individual) record in the CMS NPPES registry.

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Source: CMS NPPES (public data). Snapshot 2026-07-13. Provider record last updated 2026-04-21.