In 1981 New Jersey adopted a law requiring a mandatory minimum prison sentence for use or possession of a firearm in a variety of crimes. New Jersey firearms homicides as a per cent of all New Jersey homicides increased from 1974 to 1980 and decreased from 1981 through 1986. No similar change was observed for homicides in the balance of the U.S. or for suicides in New Jersey or the balance of the U.S. The findings suggest an effect of the mandatory minimum sentencing law on firearms homicides.