In 2006, the state of New York imposed mandated additional prison time for any crime committed with a firearm and increased the mandated minimum jail time for anyone carrying a firearm illegally. Using several different estimation strategies, we find that robberies immediately declined compared with other U.S. states once these enhancements were enacted. Other crimes, which are less likely to be committed with a firearm, were unaffected. The most plausible explanation is that criminals were deterred from committing robberies using a firearm because of the cost associated with additional prison time.