Autism and Childhood-onset Schizophrenia have been clearly defined as neuropsychiatric disorders since the studies of Kolvin and Rutter. In the early seventies the discussion on a possible overlap between the two types of disorders vanished, but nowadays this issue revives. Amongst all the advances of the DSM diagnostic criteria, the omission of developmental information appears to be a disadvantage. The Pervasive Developmental Spectrum is a broad spectrum, that with exceptions for Autism and some other characteristic disorders, to a large extent consists of an ill-defined restcategory. Most patients actually belong to this last category , the so-called PDD-NOS group. In recent years more has been published about the subgroups within this large group. One of these subgroups, the Multiple Complex Developmental Disorder (MCDD), appears to be a well defined category of patients whose validity has been confirmed by research. In adulthood, a large percentage of this MCDD group seems to develop Schizophrenia or a Schizophrenia related disorder. This again does arise the question of a possible overlap. This discussion is even emphasized by reports notably on -mostly retrospective- studies of premorbid autistic features in patients with Schizophrenia.