The study population was identified by random sampling from a computerized registry of all persons who purchased a handgun from a licensed firearms dealer in California in 1977, the first year such a registry was compiled. A total of 5,923 authorized purchasers of handguns in California in 1977 who were younger than 50 years old were identified by random sampling. The main outcome measures were incidence and relative risk (RR) of first charges for new criminal offenses after handgun purchase. Of the 5,923 authorized purchasers, 3,128 had at least one conviction for a misdemeanor offense prior to a handgun purchase, and 2,795 had no prior criminal history. Follow-up to the end of the 15- year observation period or to death was available for 77.8 percent of study subjects and for a median 8.9 years for another 9.6 percent. Handgun purchasers with at least one prior misdemeanor conviction were more than seven times as likely as those with no prior criminal history to be charged with a new offense after a handgun purchase (RR, 7.5; 95 percent confidence interval [CI], 6.6-8.7). Among men, those with two or more prior convictions for misdemeanor violence were at greatest risk for nonviolent firearm-related offenses such as weapon carrying (RR, 11.7; 95 percent CI, 6.8-20.0), violent offenses generally (RR, 10.4; 95 percent CI, 6.9-15.8), and Violent Crime Index offenses (murder or nonnegligent manslaughter, forcible rape, robbery, or aggravated assault) (RR, 15.1; 95 percent CI, 9.4-24.3); however, even handgun purchasers with only one prior misdemeanor conviction and no convictions for offenses that involved firearms or violence were nearly five times as likely as those with no prior criminal history to be charged with new offenses that involved firearms or violence. 5 tables and 32 references