This study was undertaken to evaluate trends and toxicity of pediatric methylphenidate exposures; 1993 to 1999 national poison center data were analyzed. There were 12,917 exposures, increasing from 927 in 1993 to 2,445 in 1999. The majority of children during the entire study period experienced no effect (60.3%) or minor effects (28.7%), with no fatalities. Most common reasons were unintentional general or therapeutic errors in children under 13 years and suicide attempt in adolescents. Adolescents were more likely to experience clinical toxicity, hospitalizations and more serious outcomes. The trend of increasing frequency of methylphenidate exposures reported to poison centers exactly parallels increasing therapeutic use.