The study contributes to the literature by distinguishing between illegal and legal gun availability and by using a comprehensive measure of gun crime. Results show a strong positive relationship between illegal gun availability and violent crime, gun crime, and juvenile gun crime. Little or no effect for the legitimate gun availability measure was observed in any of the estimated models. Findings also show that illegal guns had little influence on violent crimes committed with a knife. Offenders apparently were not substituting knives or other cutting instruments when illegal firearms became less available. A supplemental analysis showed no evidence of simultaneity between gun availability and violent crime. The strong and consistent effect of illegal rather than legal gun availability on violent crime has important policy implications; this suggests that greater attention should be given to devising ways for legitimate gun owners to better secure their weapons. 2 tables, 2 figures, 10 notes, and 54 references