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GILLIAN BRENNAN
NPI 1174782437
Pediatrics - Neonatal-Perinatal Medicine in Chicago, IL

Active since June 03, 2008PECOS Enrolled
5841 S MARYLAND AVE, CHICAGO, IL 60637(888) 824-0200 Get Directions Write a Review

NPPES record last updated: October 24, 2022. Verified against the NPPES registry weekly; last sync: October 18, 2026.

Record update history: Oct 24, 2022, May 19, 2022, Apr 18, 2022 and 2 more (5 updates tracked since 2017).

About Gillian Brennan NPPES

Official registry information on file with the National Plan and Provider Enumeration System.

GILLIAN BRENNAN (NPI 1174782437) is an individual neonatal-perinatal medicine provider in Chicago, Illinois, licensed in Illinois (036122278) and active in the NPI registry since June 2008. She is enrolled in Medicare PECOS and is a graduate of Other (2004).

NPPES Registry Identity

NPI1174782437
Entity TypeIndividualFemale
Primary Taxonomy2080N0001X
Provider Legal NameGILLIAN BRENNAN
Location Address5841 S MARYLAND AVEChicago, IL 60637-1443
Mailing Address150 Harvester Dr, Suite 300Burr Ridge, IL 60527-5919
Phone(888) 824-0200
Sole ProprietorNo
Medical School CMSOtherGraduated 2004
Enumeration DateJune 3, 2008
Last NPPES UpdateOctober 24, 20225 updates tracked since enumeration
✔ NPI 1174782437 is a valid, active identifier and passes the ISO check-digit test.

Specialties & Licenses

★ Primary SpecialtyPediatrics · Neonatal-Perinatal MedicineAllopathic & Osteopathic Physicians
Taxonomy Code2080N0001X
License✔ Licensed in IL · 036122278
Definition
A pediatrician who is the principal care provider for sick newborn infants. Clinical expertise is used for direct patient care and for consulting with obstetrical colleagues to plan for the care of mothers who have high-risk pregnancies.
5841 S MARYLAND AVE, Chicago, IL 60637
Open in Google Maps ↗

Medicare Participation & PECOS CMS

Medicare enrollment, assignment, billing reassignment, and ordering and referring status from CMS.

Medicare Enrollment Status

✔

Enrolled in Medicare (PECOS)

Gillian Brennan is registered in the CMS Provider Enrollment, Chain and Ownership System (PECOS).

PECOS PAC ID2961659057
PECOS Enrollment IDI20251013002859
Eligible to Order & Refer✔ Part B Labs & Imaging✔ Durable Medical Equipment✔ Home Health Agency✔ Power Mobility DevicesPer the CMS Ordering and Referring file. Eligibility means Medicare pays claims that this provider orders or refers for these categories.

Medicare Billing Reassignments

4

Medicare enrollment records show Gillian Brennan reassigns Medicare billing to 4 organizations. Each organization bills Medicare for the services this provider delivers there; the nearest is listed first.

University Of Chicago
Same address
Multi-Specialty
5841 S MARYLAND AVE, UCPG/MC 1099
Chicago, IL 60637
  • Reassigned Medicare billing, Illinois enrollment
  • 2,237 clinicians in this Medicare group
NPI 1821048786 (773) 702-9200
Osf Healthcare System
6.5 mi
General Acute Care Hospital
2800 W 95TH ST
Evergreen Park, IL 60805
  • Reassigned Medicare billing, Illinois enrollment
  • 183 clinicians in this Medicare group
NPI 1215572045 (708) 422-6200
Osf Multi-Specialty Group
128 mi
Internal Medicine
8600 N STATE ROUTE 91
Peoria, IL 61615
  • Reassigned Medicare billing, Illinois enrollment
  • 2,944 clinicians in this Medicare group
NPI 1154908929 (309) 683-5050
Guam Memorial Hospital
General Acute Care Hospital
850 GOVERNOR CARLOS CAMACHO ROAD
Oka Tamuning, GU 96913
  • Reassigned Medicare billing, Guam enrollment
  • 320 clinicians in this Medicare group
NPI 1366519027 (671) 647-2937

Source: CMS Revalidation Reassignment List, October 2026 release. Reassignment records can lag staffing changes; confirm a current affiliation with the organization.

Other Providers at the Same Location NPPES 20

Providers registered at the same practice address, or within the immediate area, according to the NPPES registry.

DR. DON MARTINEZ M.D.
Radiology (Diagnostic Radiology)
5841 S MARYLAND AVE
CHICAGO, IL 60637
Cook County (773) 926-8318
ALEXANDRA DUMITRESCU
Internal Medicine
5841 S MARYLAND AVE
CHICAGO, IL 60637
Cook County (888) 824-0200
PELEG HOROWITZ
Neurological Surgery
5841 S MARYLAND AVE
CHICAGO, IL 60637
Cook County (888) 824-0200
SANDEEP GURBUXANI
Pathology (Hematology)
5841 S MARYLAND AVE
CHICAGO, IL 60637
Cook County (888) 824-0200
DR. NIREN GANDRA M.D.
Internal Medicine
5841 S MARYLAND AVE
CHICAGO, IL 60637
Cook County (773) 702-0240
ALLIE DAKROUB MD MS
Internal Medicine
5841 S MARYLAND AVE
CHICAGO, IL 60637
Cook County (773) 702-1000
SCOTT VASHER MD
Internal Medicine (Pulmonary Disease)
5841 S MARYLAND AVE
CHICAGO, IL 60637
Cook County (773) 702-1000
DR. NATHAN CHARLES NOWALK M.D.
Internal Medicine (Pulmonary Disease)
5841 S MARYLAND AVE
CHICAGO, IL 60637
Cook County (888) 824-0200

Frequently Asked Questions NPPES & CMS

Common questions about this NPI record, answered from the official NPPES registry and CMS datasets shown on this page.

What is Gillian Brennan's NPI number?

The NPI number for Gillian Brennan is 1174782437. It was assigned to this individual provider in the NPPES registry on June 3, 2008.

Where is Gillian Brennan located?

Gillian Brennan practices at 5841 S Maryland Ave, Chicago, IL 60637. The listed phone number is (888) 824-0200.

What is Gillian Brennan's specialty?

The primary specialty registered for this NPI is Pediatrics, specializing in Neonatal-Perinatal Medicine, with taxonomy code 2080N0001X.

Is Gillian Brennan enrolled in Medicare?

Yes. Gillian Brennan is registered in the Medicare PECOS enrollment system.

Which organizations bill Medicare for Gillian Brennan's services?

According to the CMS Revalidation Reassignment List (October 2026 release), Gillian Brennan reassigns Medicare benefits to 4 organizations: University Of Chicago (Chicago, IL), Osf Healthcare System (Evergreen Park, IL), Osf Multi-Specialty Group (Peoria, IL) and Guam Memorial Hospital (Oka Tamuning, GU). Each reassignment is filed with Medicare on form CMS-855R, signed by both the clinician and the organization, and lets the organization bill Medicare and receive payment for Gillian Brennan's services. Reassignment records can lag staffing changes; confirm current arrangements with the organization.

When was this NPI record last updated?

The NPPES record for Gillian Brennan was last updated on October 24, 2022. NPI Profile syncs weekly with the NPPES registry data releases published by CMS. This NPI record was last updated 3 years ago. If this record has changed at CMS more recently, you can request an on-demand re-check against the live CMS registry, directly from this page.