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

Dr. Frederick Richard Stack, MD

Internal Medicine Physician in Sioux City, IA · enumerated 2005.

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

National Provider Identifier

1548256977

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Registry record

Entity type Individual (Type 1)

Name Dr. Frederick Richard Stack

Credential MD

Sex Male

Practice address Sioux City, IA, 51101

Phone (712) 279-2010

Fax (712) 279-2034

Enumeration date Sep 21, 2005

Last updated in NPPES Jan 28, 2026

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 91977 (MT) Secondary

207R00000X Internal Medicine Physician Allopathic & Osteopathic Physicians · License MD-46368 (IA) Primary

174400000X Specialist Other Service Providers · License 24459 (AZ) Secondary

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
436693002	Medicaid	AZ	-
AZ0866740	Other	AZ	BLUE CROSS BLUEE SHIELD
110208816	Other	AZ	MEDICARE RAILROAD

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

Is this the official NPI registry?

No. NPI Portal is a private site built on public CMS NPPES data. The official registry is npiregistry.cms.hhs.gov, operated by CMS.

What specialty is Frederick Stack?

Frederick Stack is registered in NPPES with the primary taxonomy of Internal Medicine Physician. The taxonomy code describes the provider's classification and area of specialization for claims and credentialing.

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Source: CMS NPPES (public data). Snapshot 2026-07-13. Provider record last updated 2026-01-28.