Objectives: (1) To examine U.S. national trends in the use of concomitant pharmacotherapy with the stimulant class of psychotropic drugs in youth; and (2) to present these trends in the context of (a) extant safety and efficacy data, and (b) overall trends in concomitant pharmacotherapy with psychotropic drugs for youth. Methods: Prescribing data for youths under age 18 years from National Ambulatory Medical Surveys from 1993 to 1998 were analyzed. The visits were categorized into monotherapy (only one psychotropic prescribed) and concomitant pharmacotherapy (greater than 1 psychotropic prescribed). The proportions of these groups were computed as a percentage of all visits during which a psychotropic medication was prescribed. Differences in proportions between surveys were analyzed to determine trends. Results: Between 1993-94 and 1997-98, the proportions of visits for concomitant pharmacotherapy in association with the stimulant class increased nearly five-fold. This increase paralleled an overall increase in the proportion of visits involving prescription of more than one psychotropic medication among youth. Conclusions: The growth in concomitant pharmacotherapy with the stimulants class has out-paced the increase in safety/efficacy data to inform the use of this practice, resulting in a mismatch between trends in prescribing and growth in knowledge. A simultaneous trend of note is the overall increase in the use of concomitant pharmacotherapy with all psychotropic drugs in youth. Controlled trials are particularly needed to support commonly used combinations of stimulants with antidepressants in youth. In the absence of definitive data, clinical guidelines based on expert consensus and limited data are available and are useful. (Contains 3 tables.)