Asperger's disorder is a pervasive development disorder. It involves qualitative disorders in social relationship and communication as well as restricted and repetitive interests and activities, with no delay in language acquisition. Although Asperger's disorder is an illness that begins in childhood, its diagnosis may frequently not be done until later stages. The case presented is about a 21 year old man with a diagnosis of schizoaffective disorder who, after several admissions, was sent to the Rehabilitation Hospital Unit for stabilization and diagnostic study given the atypical features of his case. The psychopathological examination showed disorders in social relationships, psychomotricity and communications that had begun in his childhood. All these data, and the results of the biomedical and psychological diagnostic tests oriented us towards the presence of a dual diagnosis of Asperger's disorder and schizoaffective disorder. The presence of common symptoms between the AD and other psychiatric diseases as well as the possible existence of comorbidity may lead to an incorrect or late diagnosis.