Objective: This study examined the child, parent, and service factors associated with polypharmacy in adolescents and young adults with autism spectrum disorders (ASD). Methods: As part of an online survey examining health service utilization patterns among individuals with ASD, parents provided demographic and clinical information pertaining to their child. This included information on current medication use, as well as information on clinical services received, clinical history, and parent well-being. Analyses examined the bivariate association between individual child, parent, and service variables and polypharmacy. Variables significantly associated with polypharmacy were included in a multiple variable logistic regression. Results: Of the 363 participants sampled, similar to 25% were receiving two or more psychotropic drugs concurrently. The patient's psychiatric comorbidity, history of hurting others, therapy use, and parent burden were predictors of polypharmacy. Conclusions: Adolescents and young adults with ASD are a highly medicated population with multiple factors associated with psychotropic polypharmacy. Although there may be circumstances in which polypharmacy is necessary, a richer understanding of what predicts polypharmacy may lead to targeted interventions to better support these individuals and their families. Findings also highlight the need to support families of children with ASD prescribed multiple psychotropic medications.