This paper examines the hypothesis that crime rates and the availability of firearms form a “vicious circle,” so that increases in one lead to increases in the other. Two waves of panel data are used to estimate the relationship between rates of robbery and the relative availability of guns in a sample of large U.S. cities. The results indicate that total robbery rates and gun availability had no influence on each other, but that weapons choice in robbery and gun availability did form a mutually reinforcing cycle. Some implications of these findings are considered.