Various personality and psychological testing procedures, as well as computed tomography scans and electroencephalograms, were employed with a sample of 18 men who had killed and faced charges of murder or manslaughter. The 18 men were compared to 21 men facing nonhomicidal violence charges and to 16 men charged with nonviolent, nonsex offenses. Results showed that more neuropathology was found in killers and assaulters than in controls and that considerable personality pathology occurred in all groups. Violent offenders scored higher on the Michigan Alcoholism Screening Test and were more likely to experience alcohol and drug-related mood dysphoria. Neuropsychological variables were significant in 20 to 25 percent of violent offenders. Killers were more like nonhomicidal violent offenders than nonviolent offenders. Specific personality variables were not significant in homicide cases; killers experienced problems but only a few were psychotic or depressed. Alcohol abuse was an important variable in the homicidal group. The interaction of neuropsychological, personality, and substance abuse variables is discussed. 122 references and 4 tables