Recognition of the autistic spectrum disorders is becoming more widespread amongst basic scientists, clinicians, and the general population. The term does not imply anything about pathology or aetiology, although it has proved to be a useful concept clinically. From Kanner's classical autism the concept has widened in scope to include milder and more subtle impairments. From a clinical perspective, there are many alternative diagnoses in an individual with autistic-like symptoms, and thorough investigation is necessary to exclude these.