Objective: To evaluate the efficacy and tolerability of modafinil in children and adolescents, ages 7 to 17, with attention-deficit/hyperactivity disorder (ADHD). Method: In this 9-week, double-blind, flexible-dose study, patients were randomized to once-daily modafinil (170-425 mg) or placebo. Assessments included ADHD Rating Scale-IV (ADHD-RS-IV) School and Home Versions and Clinical Global Impression of Improvement (CGI-I) scale. Results: Two hundred patients were randomized. Modafinil produced significant reductions in ADHD-RS-IV total scores at school (n = 128; mean change plus or minus SD: -17.5 plus or minus 13.1 points) compared with placebo (n = 66; -9.7 plus or minus 10.3 points; p less than 0.0001). Similarly, modafinil reduced ADHD-RS-IV total scores at home compared with placebo (-17.6 plus or minus 13.3 versus -7.5 plus or minus 11.8 points; p less than 0.0001). Fifty-two percent of patients randomized to modafinil and 18% of those randomized to placebo met prestudy criteria for responder on the CGI-I (p less than 0.0001). Randomization to modafinil was associated with significantly more insomnia, headache, decreased appetite, and weight loss than randomization to placebo, but discontinuation attributed to adverse events did not differ statistically between treatment groups (modafinil, 5%; placebo, 6%). Conclusion: Modafinil was well tolerated and reduced ADHD symptoms at school and home compared with placebo. (Contains 3 figures and 4 tables.)