The analysis used accident data from Tennessee and two comparison states without mandatory jail penalties, Alabama and Kentucky. Data were also gathered to determine driver awareness of the mandatory jail law and whether the law has had any effect on the self-reported drinking-driving behavior. The recidivism analysis examined the recidivism rates of Tennessee drivers convicted of drunk driving before and after the mandatory jail law. In addition, case studies were conducted in Chattanooga and Nashville. Results showed that the jail sanction had an initial effect on drunk-driving recidivism in Tennessee, but no measurable effect on alcohol-related crashes. More testing of mandatory jail is recommended, in conjunction with a major continuing program of public information to determine the general deterrent effect. Before these study results are complete, States should be cautious regarding the adoption of mandatory jail as a sanction for drunk driving. Figures, tables, and study instrument