OBJECTIVES: Aripiprazole and risperidone are the only two FDA-approved drugs for treating autism. No study has looked at their actual use and their costs in real-world settings. This will be the first study to examine the actual use of aripiprazole and risperidone in children with autism using insurance claims data. METHODS: Nationwide 2008-2010 insurance claims data from the MarketScan research database were used. Privately insured children with autistic spectrum disorders (ASD) were identified using diagnosis codes. Costs were measured as what insurance companies paid. RESULTS: Though aripiprazole became the second approved antipsychotic drug for autism in 2009 after risperidone in 2002, the rate of aripiprazole use in 2010 (30%) barely increased from that in 2008 (27%) before the approval, which nevertheless was a huge jump from a rate of less than 5% in 2003 reported in another study. The rate of risperidone use (47%) was not affected after the approval of aripiprazole. The first generic formulation of risperidone was approved in mid-2008, and generic risperidone use instantly went from zero to 50% within one month, reaching 90% by mid-2009. The average aripiprazole cost per child increased from $2986 in 2008 to $3534 in 2010, whereas the average risperidone cost decreased from $1481 in 2008 to $715 in 2010 due to use of the generic formulation. CONCLUSIONS: Because use of aripiprazole only minimally increased after approval suggests that the market for aripiprazole in autism may have been close to saturation before approval due to off-label use. In contrast, patients and clinicians responded immediately to the debut of generic risperidone by switching to it from the same branded drug, but they did not switch from the more expensive branded aripiprazole to generic risperidone, even though the literature suggests similar efficacy and safety of the two drugs for autism.