OBJECTIVES: Underuse of clozapine, an evidence-based practice, and overuse of non-clozapine antipsychotic polypharmacy (hereafter, antipsychotic polypharmacy), an unsupported practice to treat patients with schizophrenia may result in undesirable consequences. This study evaluated provider-level prevalence of clozapine and antipsychotic polypharmacy prescribing and associated factors. METHODS: Using 2010-2012 data from Pennsylvania’s Medicaid we identified all providers who regularly prescribed antipsychotics to non-elderly adult patients with schizophrenia (defined as ≥10 patients/year). We characterized providers’ patients and payers (managed care vs. fee-for-service) using Medicaid data, and providers’ demographics using CMS’s NPI file. We measured provider-level share of patients with clozapine use and antipsychotic polypharmacy use per year. Antipsychotic polypharmacy was defined as more than 90 days’ concurrent use of ≥2 non-clozapine antipsychotics, with 32-day gap allowance. We used generalized estimating equations with a binomial distribution and a logit link to examine clozapine and antipsychotic polypharmacy practices and associated patient- and provider-level factors. RESULTS: The analytic cohort included 632-650 prescribers per year. Provider-level clozapine and antipsychotic polypharmacy practices were relatively stable over time. In 2012, provider-level mean shares of patients with clozapine and antipsychotic polypharmacy use were 6.9% (range: 0%-88.9%) and 7.0% (range: 0%-45.2%), respectively. A sizable proportion of providers prescribed antipsychotic polypharmacy but not clozapine (e.g., 15.5% in 2012). High volume prescribers were much more likely to prescribe clozapine (OR = 1.43, p<0.01) and antipsychotic polypharmacy (OR = 2.65, p<0.01) than low volume prescribers. Primary care providers were substantially less likely than psychiatrists to prescribe clozapine (OR = 0.55, p<0.01) but just as likely to antipsychotic polypharmacy. CONCLUSIONS: Antipsychotic polypharmacy is used as much as clozapine in the care of Medicaid beneficiaries with schizophrenia, but many prescribers only use the former. Clinical and policy initiatives are needed to improve providers’ knowledge of clozapine and increase its use while decreasing use of antipsychotic polypharmacy.