Despite prominent attentional symptoms in Pervasive Developmental Disorders (PDD) the relationship between PDD and Attention Deficit Hyperactivity Disorder (ADHD) has received little direct examination. In addition, outcome studies of children with PDD often focus on language, educational placement, or adaptive skills, but seldom on loss of the PDD diagnosis or change to another clinical syndrome. We present three cases in detail, and tabular data on eight more, that illustrate a clinical presentation in which prototypical cases of PDD evolve into clear-cut cases of ADHD from early to middle childhood.