Quick answers
- Does Jacek Zajac accept Medicare assignment?
- Yes. Medicare's clinician data says Jacek Zajac accepts Medicare assignment (the Medicare-approved amount as full payment for covered services), as of October 2, 2026. Ask the office to confirm before your visit.
- How many Medicare patients does Jacek Zajac see?
- In 2024, CMS data shows 444 Original Medicare patients and 1,206 services for Jacek Zajac. This counts Original Medicare only and measures volume, not quality.
- What is Jacek Zajac's NPI number?
- 1396817912. The NPI (National Provider Identifier) is the clinician's permanent federal ID; you can look it up in the official NPI Registry.
Medicare activity in 2024
Official CMS public-use data for Jacek Zajac, data year 2024 (released May 21, 2026). It covers Original Medicare (fee-for-service) patients only, not Medicare Advantage or other insurance. It shows volume, not quality or outcomes. CMS hides any count of 10 or fewer patients.
| Original Medicare patients | 444 |
|---|---|
| Services billed to Medicare | 1,206 |
| Different services or procedures | 15 |
| Participating Medicare provider | Yes |
| Average age of these patients | 75 |
Most frequent services
- Established patient office or other outpatient visit with moderate level of decision making, if using time, 30 minutes or more (99214)555 services
- Subsequent hospital care with moderate levelof medical decision making, if using time, at least 35 minutes (99232)361 services
- Established patient office or other outpatient visit with low level od decision making, if using time, 20 minutes or more (99213)100 services
- Initial hospital care with moderate level of medical decision making, if using time, at least 75 minutes (99223)57 services
- Initial hospital care with straightforward or low-level medical decision making, if using time, at least 55 minutes (99222)33 services
Chronic conditions among these patients
Share of this clinician’s Original Medicare patients with each condition, as published by CMS (it describes the patients, not the care given).
- High blood pressure75%
- High cholesterol75%
- Diabetes65%
- Arthritis48%
- Ischemic heart disease47%
- Chronic kidney disease42%
Hospitals where Jacek Zajac works
Medicare's Facility Affiliation Data lists Jacek Zajac at these hospitals (updated October 2, 2026). Each hospital page shows its address, phone, emergency services, Medicare rating and all its clinicians. Star rating and emergency services: Hospital General Information (CMS), data updated October 26, 2026.
- Advocate Good Samaritan HospitalDowners Grove, IL · Acute Care Hospital · Medicare rating: 4 of 5 stars · Emergency services: listed by Medicare · CCN 140288
- Advocate Illinois Masonic Medical CenterChicago, IL · Acute Care Hospital · Medicare rating: 3 of 5 stars · Emergency services: listed by Medicare · CCN 140182
- Advocate Lutheran General HospitalPark Ridge, IL · Acute Care Hospital · Medicare rating: 4 of 5 stars · Emergency services: listed by Medicare · CCN 140223
- Edward HospitalNaperville, IL · Acute Care Hospital · Medicare rating: 3 of 5 stars · Emergency services: listed by Medicare · CCN 140231
- Elmhurst Memorial HospitalElmhurst, IL · Acute Care Hospital · Medicare rating: 3 of 5 stars · Emergency services: listed by Medicare · CCN 140200
Practice locations
Addresses where Jacek Zajac is enrolled with Medicare (CMS data updated October 2, 2026).
- 155 E Brush Hill Rd, Elmhurst HospitalElmhurst, IL 60126 (331) 221‑1000
- 2500 S Highland Ave, Suite 104Lombard, IL 60148 (630) 629‑3610
Group practices
Medicare enrollment lists Jacek Zajac as a member of this group (CMS data updated October 2, 2026).
- Endocrinology Associates SC2 clinicians in the group
Specialties
- Endocrinologyprimary
Other endocrinologists in Elmhurst
Clinicians with the same Medicare primary specialty in Elmhurst, IL — not a recommendation.
Other clinicians in Endocrinology Associates SC
Medicare enrollment lists these clinicians in the same group practice — not a recommendation.
Clinician information
| Credential | MD |
|---|---|
| Graduation year | 1991 (35 years since medical school) |
| Gender (as listed) | Male |
| Medicare assignment | Accepts (Medicare-approved amount as full payment) |
| NPI (National Provider Identifier) | 1396817912 |
| Corrections | Report an error or suggest an update → |
Most corrections must be made at the source: clinicians update their NPI Registry record (NPPES) and their Medicare enrollment (PECOS); this page follows the next data release.
Sources
- Facility Affiliation Data — Centers for Medicare & Medicaid Services (CMS), data updated October 2, 2026, retrieved October 29, 2026
- Hospital General Information — CMS, data updated October 26, 2026, retrieved November 13, 2026
- National Downloadable File (Doctors and Clinicians) — CMS, data updated October 2, 2026, retrieved October 29, 2026
- Medicare Physician & Other Practitioners - by Provider — CMS, data year 2024, released May 21, 2026; Medicare Physician & Other Practitioners - by Provider and Service
- NPI Registry — U.S. Department of Health and Human Services (NPPES), the clinician’s official record
- Medicare Care Compare — official Medicare tool to look up clinicians