A Maryland law banning the sale of assault pistols and high-capacity ammunition magazines took effect in June 1994. Other states, including California, New Jersey and Connecticut, and the federal government have enacted bans on the sale and possession of various assault weapons. We assessed the initial impact of the Maryland law on the use of assault pistols in association with criminal activity and found that fewer assault pistols than would have been expected without the ban were used in crime as measured by the number of assault pistols recovered by the Baltimore City Police Department.