The law, preserved the general structure of Massachusetts gun control statutes, adding only a mandatory minimum 1-year sentence for those convicted of illegally carrying a firearm. The new law also prohibited suspended sentences, probation, and various informal means of avoiding sentencing. A 2-year study of the law's effects, based on assessment of crime statistics from both the FBI and the Boston Police Department, evaluation of arrest reports, examination of court records, and interviews with criminal justice personnel, revealed that the law did influence the crime rate. The law had a moderate deterrent effect on gun robberies and homicides. The law also caused a decrease in the proportion of defendants who were convicted of illegally carrying a firearm. The proportion of defendants who received some jail sentence increased. In general, judges and prosecutors did not feel that the law facilitated harsher treatment of those who committed violent crimes. Seventeen references and extensive figures and tables are provided.