We studied the risk of homicidal behavior among 281 released male forensic psychiatric patients during the 14-year period 1978-1991. Released patients were about 300 times more likely to commit a homicide than the general male population during the first year outside hospital, and the corresponding risk was 53-fold during a mean follow-up period of 7.8 years. The odds ratio for committing a homicide among all Finnish schizophrenics during the 12-year period 1980-1991 was 9.7, which indicates that previous criminality associated with schizophrenia also increases the risk of homicidal behavior remarkably when compared with schizophrenia per se. We believe that this kind of epidemiological approach is a useful method of identifying and classifying factors associated with very high risk of homicidal behavior and preventing homicidal behavior among high-risk populations.