Objective: To examine patterns and recent trends in multiclass psychotropic treatment among youth visits to office-based physicians in the United States. Method: Annual data from the 1996-2007 National Ambulatory Medical Care Surveys were analyzed to examine patterns and trends in multiclass psychotropic treatment within a nationally representative sample of 3,466 child and adolescent visits to office-based physicians in which a psychotropic medication was prescribed. Results: There was an increase in the percentage of child visits in which psychotropic medications were prescribed that included at least two psychotropic classes. Across the 12 year period, multiclass psychotropic treatment rose from 14.3% of child psychotropic visits (1996-1999) to 20.2% (2004-2007) (adjusted odds ratio [AOR] = 1.89, 95% confidence interval [CI] = 1.22-2.94, p less than 0.01). Among medical visits in which a current mental disorder was diagnosed, the percentage with multiclass psychotropic treatment increased from 22.2% (1996-1999) to 32.2% (2004-2007) (AOR = 2.23, 95% CI = 1.42-3.52, p less than 0.001). Over time, there were significant increases in multiclass psychotropic visits in which ADHD medications, antidepressants, or antipsychotics were prescribed, and a decrease in those visits in which mood stabilizers were prescribed. There were also specific increases in co-prescription of ADHD medications and antipsychotic medications (AOR = 6.22, 95% CI = 2.82-13.70, p less than 0.001) and co-prescription of antidepressant and antipsychotic medications (AOR = 5.77, 95% CI = 2.88-11.60, p less than 0.001). Conclusions: Although little is known about the safety and efficacy of regimens that involve concomitant use of two or more psychotropic agents for children and adolescents, multiclass psychotropic pharmacy is becoming increasingly common in outpatient practice. (Contains 1 figure and 3 tables.)