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The observation that almost half of the homicides committed by people with a psychotic illness occur before initial treatment suggests an increased risk of homicide during the first episode of psychosis. The aim of this study was to estimate the rates of homicide during the first episode of psychosis and after treatment. A systematic search located 10 studies that reported details of all the homicide offenders with a psychotic illness within a known population during a specified period and reported the number of people who had received treatment prior to the offense. Meta-analysis of these studies showed that 38.5% (95% confidence interval [CI] = 31.1%-46.5%) of homicides occurred during the first episode of psychosis, prior to initial treatment. Homicides during first-episode psychosis occurred at a rate of 1.59 homicides per 1000 (95% CI = 1.06-2.40), equivalent to 1 in 629 presentations. The annual rate of homicide after treatment for psychosis was 0.11 homicides per 1000 patients (95% CI = 0.07-0.16), equivalent to 1 homicide in 9090 patients with schizophrenia per year. The rate ratio of homicide in the first episode of psychosis in these studies was 15.5 (95% CI = 11.0-21.7) times the annual rate of homicide after treatment for psychosis. Hence, the rate of homicide in the first episode of psychosis appears to be higher than previously recognized, whereas the annual rate of homicide by patients with schizophrenia after treatment is lower than previous estimates. Earlier treatment of first-episode psychosis might prevent some homicides.