: To provide a clinically useful analysis of the extent to which autism and Asperger syndrome coexist with other disorders. Selective review of the literature detailing data pertaining to symptoms and disorders sometimes encountered in connection with autism or Asperger syndrome. A large number of medical conditions, psychiatric disorders and behavioural and motor dyscontrol symptoms are associated with autism and Asperger syndrome. Comorbidity is to be expected in autism spectrum disorders -directly or indirectly. Comorbid conditions may be markers for underlying pathophysiology and suggest a more varied treatment approach. There is a great need for in-depth research into this area, meaning that the exclusion criteria of current diagnostic manuals, i.e. those that rule out a diagnosis of autism in some disorders, and a diagnosis of certain other disorders in autism may have to be revised.