Data on five aggressive and/or violent human behaviors were examined by computer to determine whether a relationship exists between the lunar syndoic cycle and human aggression. Homicides, suicides, fatal traffic accidents, aggravated assaults and psychiatric emergency room visits occurring in Dade County, Florida all show lunar periodicities. Homicides and aggravated assaults demonstrate statistically significant clustering of cases around full moon. Psychiatric emergency room visits cluster around first quarter and shows a significantly decreased frequency around new and full moon. The suicide curve shows correlations with both aggravated assaults and fatal traffic accidents, suggesting a self-destructive component for each of these behaviors. The existence of a biological rhythm of human aggression which resonates with the lunar synodic cycle is postulated.