Data came from statistics published by the World Health Organization and the United Nations. The analysis used two-stage least squares regression to control for homicide’s effect on firearm availability and other confounding factors. Results revealed a statistically significant positive effect of firearm availability on national homicide rates. The magnitude of the association was considerable. Lethal violence was likely to be high in countries with greater supplies of privately owned guns. In addition, homicide rates were likely to be high in countries with ethnically heterogeneous populations and conservative welfare states. The case of the United States was consistent with the estimated model in that it is an ethnically heterogeneous country that spends relatively little on social programs and also leads the world in private firearm possession. The observed relationship was insensitive to sample composition. Results also indicated that homicide rates did not influence the levels of firearm availability. The analysis concluded that the data indicating that greater access to guns increased levels of lethal violence need cautious interpretation and that future research should focus on direct measures of firearm availability in more countries and on cross-national relationships between firearm availability and other forms of violence. Tables, footnotes, and 68 references (Author abstract modified)