An epidemiologic assessment of primary homicides in the United States for 1976 through 1979 showed the following. Sixty percent of primary homicides were male victim/male offender events; 40% involved a female as a victim and/or as an offender. Three per cent of primary homicides were female victim/female offender events; 97% involved a male as a victim and/or as an offender. Primary homicides involving female victims or offenders were more frequently intrafamilial than those involving males, but rates of intrafamilial homicides by males were greater than those involving females. The preponderance of all primary homicides occurred between acquaintances, but the relationship between victim and offender varied with age, sex, and race. The weapons used varied with the victim's and offender's age, sex, and race, and with the relationship between victim and offender. Based on the described patterns, prevention measures should be divided into three broad areas: intrafamilial violence, extrafamilial violence, and male patterns of aggression. Key target populations for the first area include females, rural households, and the very young or very old. A Key target population for the second area is teenage males. Tabular and graphic data footnotes, and 26 references are provided. (Author abstract modified)