Methylphenidate is the psychotherapeutic drug most often prescribed for the management of attention-deficit/hyperactivity disorder (ADHD) in children and adolescents. It is also used in the treatment of narcolepsy, Tourette's syndrome, and depression. Methylphenidate affects several neurotransmitters, including dopamine, norepinephrine, and serotonin. The abuse potential of methylphenidate has been recognized for years. The physiological, subjective, and behavioral effects of methylphenidate are similar to those of amphetamines. The current study queried the American Association of Poison Control Centers Toxic Exposure Surveillance System for 1993-99 data on methylphenidate abuse cases in children 10- to 19-years-old that were followed to known outcome. Main outcome measures included number of cases annually, toxicity, management site, and coded medical outcome. Of 759 cases, 42.7 percent involved 10- to 14-year-olds. For the 530 cases (70 percent) that involved methylphenidate only, the frequency increased sevenfold from 1993 to 1999. Of 570 patients (75.1 percent) managed in a health care facility, 398 were discharged from the emergency department, and 172 were admitted. Symptoms occurred more commonly in exposures that involved coingestants (84.3 percent) than in methylphenidate-only exposures (71.1 percent). The most common symptoms in adolescents with methylphenidate only were tachycardia (31.7 percent), agitation/irritability (25.7 percent), and hypertension (11.5 percent). Outcomes were "no effect" in 189 cases (24.9 percent) and mild, moderate, and severe in 318 (41.9 percent), 245 (32.3 percent), and 7 (0.9 percent) patients, respectively. Overall, the poison center data show the increasing frequency of methylphenidate abuse. Although the majority of adolescents experienced clinical effects from the abuse and were managed in a health care facility, outcomes were good, especially in cases that involved methylphenidate only. 3 tables, 2 figures, and 23 references