Background: As a result of the increased public interest in autism spectrum disorders (ASD), certain core manifestations of ASD--impaired social interaction and communication, bizarre interests--are now commonly recognized as being typical of autism, not only in children, but in adults as well. More often than before, general practitioners, neurologists, and psychiatrists find themselves being asked whether a patient is suffering from previously unrecognized Asperger syndrome (AS). The prevalence of ASD is estimated at 1%, and the ratio of diagnosed to undiagnosed cases at about 3:2. Little is known about the diagnostic evaluation of AS in adulthood.

Method: We selectively searched the Medline database for pertinent literature, paying special attention to diagnostic manuals and to the guideline of the United Kingdom's National Institute for Health and Care Excellence (NICE).

Results: Centrally important aspects of the diagnosis of AS include an assessment of the patient's ability to assume the emotional perspectives of others, non-verbal modes of expression, repetitive behavior patterns, and childhood social behavioral history. The autism quotient (AQ) is now established as a simple but nonspecific screening test. Up to 70% of all affected adults have comorbid disturbances, most often depression and anxiety disorders. The differential diagnosis includes personality disorders, anxiety disorders, obsessive-compulsive disorder, and attention deficit-hyperactivity disorder. The diagnostic assessment should proceed in stepwise fashion, starting from simple screening in primary care and then moving on to evaluation of the suspected diagnosis by a mental health care specialist, followed by extensive further investigation in an outpatient clinic specifically devoted to patients with autism spectrum disorders.

Conclusion: The diagnostic assessment of autism in adults requires knowledge of the core and accompanying manifestations of autism and of their differential diagnoses. More research is needed for the development of further screening tests and the precise determination of diagnosis rates, differential diagnoses, nd comorbidities.