Forty-six of 93 children with neurofibromatosis type 1 (NF1) were found to satisfy the diagnostic criteria for attention-deficit-hyperactivity disorder (ADHD). Detailed comparisons were made among 20 children with NF1 and ADHD (12 males, 8 females; mean age 10.7 years, SD 2.2), 26 control children with NF1 (15 males, 11 females; mean age 11.3 years, SD 2.3), 14 control children with ADHD (7 males; mean age 9.9 years, SD 1.9), and 14 normally developing control children (7 males; mean age 11.2 years, SD 2.8). Children with NF1 and ADHD had the lowest IQ scores among the four groups. Test of Variables of Attention (TOVA) scores were poorer in the NF1-ADHD and ADHD control groups than in the two non-ADHD groups. Those with NF1 and ADHD were rated significantly poorer on the Child Behavior Checklist (CBCL) than were the NF1 control group. By administrating low doses (5 to 15 mg) of methylphenidate to the NF1-ADHD group, significantly improved TOVA scores were obtained. One-year follow-up yielded significantly improved CBCL scores. Our results show a high incidence of ADHD in NF1 and support an association between ADHD and learning and social problems in children with NF1. It was demonstrated that stimulant medication can lead to improvement in cognitive, academic, and social problems of children with NF1 and ADHD.