Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder with an estimated prevalence of 1/2190 to 1/6711. Attention deficit hyperactivity disorder (ADHD) has been reported to be common in NF1. We, the researchers at Hospices Civils de Lyon, designed a randomized, double blind, placebo controlled, crossover trial with a total follow-up duration of 9 weeks to evaluate the effect of methylphenidate (MPH) on the improvement on the simplified parents Conners' Rating Scale. In a parallel exploratory study we will compare the nature of attention deficit disorders in NF1 children to 30 ADHD NF1-free controls. Children aged 7 to 12 years are eligible when their intelligence quotient (IQ) is between 80 and 120. Fifty subjects (25 for each period) were required for testing the primary study hypothesis.