The authors studied the relationship of EEG abnormalities and violent criminal behavior in 222 defendants referred for psychiatric evaluation. There was no connection between the number of violent offenses and EEG abnormalities in general. Focal abnormalities, however, especially of the left hemisphere, were related to a significantly higher number of violent offenses. In many cases these abnormalities were accompanied by mental retardation, epilepsy, or earlier brain damage. The findings suggest that impairment of left hemisphere functions may enhance the propensity for violent behavior in a subgroup of offenders.