Twenty Israeli children diagnosed as having Attention Deficit Hyperactivity Disorder (ADHD) participated in the study. The study used a double-blind, cross-over, placebo-control design, in which each child received a three-week treatment of methylphenidate (MPH), and a three-week treatment with a placebo. Their teachers completed the Conners' Teacher Rating Scale (CTRS) along with ratings of other variables prior to the beginning of the study and during the two treatment periods. The subjects were tested on a specially designed battery of both cognitive and personality tests at the end of each treatment period. The results showed significant differences between ratings of children's behavior in pretest and subsequent placebo and MPH treatment periods. Comparison of the MPH and placebo treatment revealed no differences in any of the measures assessing cognitive ability and personality characteristics.