Several studies have found a high level of mental disturbance among prisoners. However, none have suggested that prison conditions may have caused the high level of disturbance shown. Studies on violence and mental disorder among mental patients suggest an elevated risk of violent offending, not a higher rate. This elevated risk is a function of prior criminality in some mental patients rather than of mental illness in itself. The literature indicates that schizophrenics have some elevated risk of violence, although the overall association between schizophrenia and violence is weak. Thus, violent behavior in schizophrenics cannot be explained by the schizophrenic state itself; paranoid and other delusional beliefs may be important. Further, only a tiny proportion of depressed people are violent. Causes of violence among the depressed and the schizophrenic must be sought in the same social and psychological variables that have determined aggression in others. The relationship between organic syndromes and violence is also questionnable. In addition, the psychopathy of a patient may not be useful in identifying violent behavior, since experts have had difficulty describing psychopathy in patients. Long-term followups of patients showing psychopathic traits indicate that psychopathy is of some use in predicting future offending and social difficulty. However, more research tying psychopathy to violent behavior is needed. An alternative to the medical model is to apply psychological models of how aggressive and sexually deviant behaviors are determined and modified. The effects of mental disorder on the propensity for aggressive behavior need to be located within a model of the processes involved in normal aggression. A chart and about 150 references are supplied.