Diagnosis and classification of autism and related pervasive developmental disorders is both easy and difficult. Infantile autism is a characteristic syndrome on which many publications have appeared in the last fifty years. Controversely, the diagnosis and even the classification of children with pervasive developmental disorders related to autism is difficult. Although children with these disorders are twice as numerous as children with infantile autism, growing attention has been directed to the latter group since the last decade.

In this paper, autism and related disorders are described as a developmental disorder as well as a spectrum disorder. The spectrum of clinical symptoms can be explained, of which infantile autism is the most severe and prototypical manifestation.

A working model is presented which accounts for all the problems of children with pervasive developmental disorders. An illustration of working with the model in practice is also given. The main lines of treatment and stages in treatment are briefly described.