WILLIAM MUSTAS, P.A. appears in the CMS NPPES registry as a Physician Assistant provider holding P.A. credentials at 1111 DELAFIELD ST STE 215, WAUKESHA, WI, 53188, with a listed phone of (262) 542-0074. NPI 1629080932 was issued on 08/13/2006. Because NPPES data is self-reported by the provider and refreshed monthly, the address, phone, and specialty reflect what MUSTAS most recently submitted to CMS rather than a vetted directory listing, which is why patients should always confirm the practice is still at this location before scheduling.

Medicare Part D records for calendar year 2023 show 959 prescription claims written by this provider, covering 352 Medicare beneficiaries and totaling roughly $102K in drug spend, split 13% brand-name and 87% generic by claim count, with an opioid prescribing rate of 4.4%. These figures capture only Medicare Part D — commercial insurance, Medicaid, and cash-pay prescriptions are not included, and any drug-beneficiary cell under 11 is suppressed by CMS for patient privacy. On the CMS Merit-based Incentive Payment System, this provider earned a Final Score of 82.3961/100 for the 2023 performance year (Quality 77.8816, Cost 74.3833), compared with the national average of 83.1.

Physician Assistant is a high-volume specialty nationwide, with 149,975 enrolled providers across 56 states and an average of 790 Part D claims per prescriber, so the context for interpreting these metrics differs meaningfully from a primary-care baseline. Important: PlainDoctor is a directory of publicly available government data, not medical advice, a malpractice database, or a quality rating. Inclusion here does not imply a recommendation, and absence of complaints or sanctions on this page does not mean none exist — always verify credentials through the NPPES NPI Registry, your state medical board, and the ABMS or AOA before making healthcare decisions.