 The purpose of this study is to develop a better tolerated and more effective pharmacologic treatment with individuals with Pervasive Developmental Disorder. This is a double-blind, placebo-controlled study of aripiprazole in the management of the maladaptive behaviors of Pervasive Developmental Disorder. The investigators hypothesize that aripiprazole will be more effective than placebo for reducing aggression,tantrum and self-injurious behavior in children with Pervasive Developmental Disorder. 