To investigate the associations among handgun regulations, assault and other crimes, and homicide, we studied robberies, burglaries, assaults, and homicides in Seattle, Washington, and Vancouver, British Columbia, from 1980 through 1986. Although similar to Seattle in many ways, Vancouver has adopted a more restrictive approach to the regulation of handguns. During the study period, both cities had similar rates of burglary and robbery. In Seattle, the annual rate of assault was modestly higher than that in Vancouver (simple assault: relative risk, 1.18; 95 percent confidence interval, 1.15 to 1.20; aggravated assault: relative risk, 1.16; 95 percent confidence interval, 1.12 to 1.19). However, the rate of assaults involving firearms was seven times higher in Seattle than in Vancouver. Despite similar overall rates of criminal activity and assault, the relative risk of death from homicide, adjusted for age and sex, was significantly higher in Seattle than in Vancouver (relative risk, 1.63; 95 percent confidence interval, 1.28 to 2.08). Virtually all of this excess risk was explained by a 4.8-fold higher risk of being murdered with a handgun in Seattle as compared with Vancouver. Rates of homicide by means other than guns were not substantially different in the two study communities. We conclude that restricting access to handguns may reduce the rate of homicide in a community.