*Inclusion criteria*

All subjects must give signed, informed consent.

Probands must have a consensus best-estimate DSM-IV (Diagnostic and Statistical Manual of Mental Disorders) diagnosis of SZ (schizophrenia) or of schizoaffective disorder with at least six months' duration of the "A" criteria for schizophrenia.

Subjects must be over 18 years of age at interview, male or female.

The informant should have known the subject for at least two years, be familiar with the psychiatric history, and have at least one hour of contact per week with the proband (close family members preferred). *Exclusion criteria*

Unable to give informed consent to all aspects of the study.

Unable to speak and be interviewed in English (to ensure validity of the interviews).

Psychosis is deemed secondary to substance use by the consensus diagnostic procedure because psychotic symptoms are limited to periods of likely intoxication or withdrawal, or there are persistent symptoms which are likely to be related to substance use (i.e., increasing paranoia after years of amphetamine use; symptoms limited to visual hallucinations after extensive hallucinogen use).

The psychotic disorder is deemed secondary to a neurological disorder such as epilepsy based on the nature and timing of symptoms. For example, non-specific, non-focal EEG abnormalities are common in SZ, but subjects with psychosis that emerged in the context of temporal lobe epilepsy would be excluded.

Subjects with severe mental retardation (MR). Subjects with mild MR (IQ is greater than or equal to 55 or based on clinical and educational history) will be included, if SZ symptoms and history can be clearly established.