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DR. WILLIAM J MESIBOV MD
NPI 1649364910
Pediatrics in Syosset, NY

Active since October 03, 2006PECOS Enrolled
50 UNDERHILL BLVD, SUITE 101, SYOSSET, NY 11791(516) 921-2122(516) 921-0670 Get Directions Write a Review

NPPES record last updated: July 8, 2007. Verified against the NPPES registry weekly; last sync: October 25, 2026.

About Dr. William J Mesibov Md NPPES

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

DR. WILLIAM J MESIBOV MD (NPI 1649364910) is an individual pediatrics provider in Syosset, New York, licensed in New York (90604) and active in the NPI registry since October 2006. He is enrolled in Medicare PECOS.

NPPES Registry Identity

NPI1649364910
Entity TypeIndividualMale
Primary Taxonomy208000000X
Provider Legal NameDR. WILLIAM J MESIBOVCredential: MD
Location Address50 UNDERHILL BLVD, SUITE 101Syosset, NY 11791-3418
Mailing Address50 Underhill Blvd, Suite 101Syosset, NY 11791-3418 · (516) 921-2122 · Fax (516) 921-0670
Phone(516) 921-2122
Fax(516) 921-0670
Sole ProprietorNo
Enumeration DateOctober 3, 2006
Last NPPES UpdateJuly 8, 2007
✔ NPI 1649364910 is a valid, active identifier and passes the ISO check-digit test.

Specialties & Licenses

★ Primary SpecialtyPediatricsAllopathic & Osteopathic Physicians
Taxonomy Code208000000X
License✔ Licensed in NY · 90604
Definition
A pediatrician is concerned with the physical, emotional and social health of children from birth to young adulthood. Care encompasses a broad spectrum of health services ranging from preventive healthcare to the diagnosis and treatment of acute and chronic diseases. A pediatrician deals with biological, social and environmental influences on the developing child, and with the impact of disease and dysfunction on development.
50 UNDERHILL BLVD, Syosset, NY 11791
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Medicare Participation & PECOS CMS

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

Medicare Enrollment Status

✔

Enrolled in Medicare (PECOS)

Dr. William J Mesibov Md is registered in the CMS Provider Enrollment, Chain and Ownership System (PECOS).

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 Reassignment

Medicare enrollment records show William Mesibov reassigns Medicare billing to 1 organization. The organization bills Medicare for the services this provider delivers there.

Optum Medical Care, P.C.
28 mi
Cardiovascular Disease
90 SOUTH BEDFORD RD, MT KISCO MEDICAL GROUP PC
Mount Kisco, NY 10549
  • Reassigned Medicare billing, New York enrollment
  • Medicare enrollment name: Optum Medical Care PC
  • 1,601 clinicians in this Medicare group
NPI 1982643003 (914) 241-1050

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

Physician Visit Costs CMS claims · ZIP area

Typical Medicare office-visit costs in the 11791 ZIP code area, from fee-for-service claims. These are area statistics, not this provider’s prices; actual charges vary by service and coverage.

New Patient
$105.06 typical visit price
range $67.40 – $203.53
Typical copayment $26.26 (range $16.85 – $50.88)
Most-billed visit code 99203
Established Patient
$117.62 typical visit price
range $21.66 – $164.45
Typical copayment $29.40 (range $5.41 – $41.11)
Most-billed visit code 99214
Amounts reflect what Medicare beneficiaries in this ZIP area are typically charged for office visits. Patients with other coverage should check their individual plans.

Other Providers at the Same Location NPPES 4

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

ANDREW RICHARD ATTIAS DDS
Dentist (Pediatric Dentistry)
50 UNDERHILL BLVD
SYOSSET, NY 11791
Nassau County (516) 921-0022
DR. LINDA H JACOBS MD
Pediatrics
50 UNDERHILL BLVD, SUITE 101
SYOSSET, NY 11791
Nassau County (516) 921-2122
REENA NANDI MD
Psychiatry & Neurology (Psychiatry)
50 UNDERHILL BLVD, SUITE 202
SYOSSET, NY 11791
Nassau County (516) 248-2085
MESIBOV AND ALTMAN LLP
Pediatrics
50 UNDERHILL BLVD, SUITE 101
SYOSSET, NY 11791
Nassau County (516) 921-2122

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 William Mesibov's NPI number?

The NPI number for William Mesibov is 1649364910. It was assigned to this individual provider in the NPPES registry on October 3, 2006.

Where is William Mesibov located?

William Mesibov practices at 50 Underhill Blvd Suite 101, Syosset, NY 11791. The listed phone number is (516) 921-2122.

What is William Mesibov's specialty?

The primary specialty registered for this NPI is Pediatrics with taxonomy code 208000000X.

Is William Mesibov enrolled in Medicare?

Yes. William Mesibov is registered in the Medicare PECOS enrollment system.

Which organization bills Medicare for William Mesibov's services?

According to the CMS Revalidation Reassignment List (October 2026 release), William Mesibov reassigns Medicare benefits to Optum Medical Care, P.C. (Mount Kisco, NY). The 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 William Mesibov'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 William Mesibov was last updated on July 8, 2007. NPI Profile syncs weekly with the NPPES registry data releases published by CMS. This NPI record was last updated 19 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.