The 460 offenders came from a random sample of 650 male inmates and were those who were interviewed and granted access to their criminal files. Those who agreed to participate were similar to those who refused with respect to age, marital status, type of offense, maternal language, number of sentences served in a penitentiary, security level of the penitentiary where their housed, major offense leading to the current sentence, and the most serious crime for which they had been convicted. The sample included 87 inmates who had been convicted of at least one first-degree murder, second-degree murder, or manslaughter. Results revealed that significantly more of the homicide offenders (35 percent) than other offenders (21 percent) suffered from a major mental disorder. In the great majority of cases, the mental disorder was present before the homicide. When single diagnoses were examined, no group differences could be identified. However, analysis of concurrent diagnoses revealed that more of the homicide offenders manifested a major depression in combination with antisocial personality disorder, alcohol or drug abuse, and/or drug dependence. The results of this and other independent studies suggest the need for further research on the link between multiple disorders and aggressive behavior. Tables, footnote, and 34 references