OBJECTIVES: This study evaluated the persistent use of psychotropic polypharmacy and characterized how well the cross-sectional operational definitions of polypharmacy used in published pediatric studies accurately identify patients’ prescribed long-term treatment. METHODS: The prevalence of psychotropic polypharmacy was defined as receiving ≥ 14 days, ≥ 30 days, ≥ 60 days, and ≥ 90 days of overlapping psychotropic prescription fills. Descriptive analysis was used to compare the prevalence findings based on Multistate Medicaid data involving children and adolescents 6 to 18 years of age. A sensitivity analysis was conducted to further explore the extent to which the cross-sectional operational definitions of polypharmacy used in published literature identified patients who were prescribed psychotropic combinations on a long-term basis.  RESULTS: Analysis of Multistate Medicaid data revealed that 218,696 children and adolescents filled at least one psychotropic prescription in 2005. Of these patients, 22.52% received psychotropic combinations for ≥14 consecutive days.  The observed rate of polypharmacy dropped to 21.07% with ≥30 days overlap criterion and to 16.44% with 60 days overlap criterion. 25%-60% of patients with polypharmacy in cross-sectional definitions were likely receiving two or more psychotropic agents on a short-term basis.. Furthermore, cross-sectional definitions failed to identify a 40% to 70% of patients on long-term polypharmacy (≥60 day overlap).   CONCLUSIONS: The long-term use of psychotropic polypharmacy in Medicaid children and adolescents in this study appeared modest. The comparison between our observations and previous studies illustrate the considerable problems that arise when comparing rates of polypharmacy across studies with inconsistent operational definitions.