Hysterical symptoms are defined as complaints that are not fully explained by organic or functional neurological disease. Hysterical symptoms are common in neurological practice, accounting for about 1% of neurological diagnoses. Of those with neurological hysterical symptoms, about 80% will not have the hysterical personality, and about 80% will not have Briquet's hysteria. Some 60% will have a physical disease and perhaps as many as 50% will have recognizable psychiatric illness, particularly depression. Others may have unrecognized physical or psychiatric illness. Many hysterical symptoms may be understood in terms of abnormal illness behaviour.