Schizophrenia is a disorder in which patients have psychotic symptoms and social and/or occupational dysfunction that persists for at least 6 months.

Schizophrenia affects I % of the population. The typical age of onset is the early 20s for men and the late 20s for women. Women are more likely to have a "first break" later in life; in fact, about one third of women have an onset of illness after age 30. Schizophrenia is diagnosed disproportionately among the lower socioeconomic classes; although theories exist for this finding, none have been substantiated.

The etiology of schizophrenia is unknown. There is a clear inheritable component, but familial incidence is sporadic and schizophrenia does occur in families with no history of the disease. Schizophrenia is widely believed to have a neurobiological basis.    

Delusional disorder is characterized by nonbizarre delusions without other psychotic symptoms. It is rare, its course is chronic, and treatment is supportive.

This disorder is rare, with a prevalence of <0.05%. Generally, onset is in middle to late life; it affects women more often than men. Its course is chronic and unremitting.

The etiology is unknown. Often, psychosocial stressors appear to be etiologic, for example, following migration. In migration psychosis, the recently immigrated person develops persecutory delusions. Many patients with delusional disorder have a paranoid character premorbidly. Paranoid personality disorder has been found in families of patients with delusional disorder.