The purpose of this study is to evaluate the deterrent effect of imprisonment. Using data on offenders convicted of felonies in 1993 in Jackson County (Kansas City), Missouri, we compare recidivism rates for offenders sentenced to prison with those for offenders placed on probation. We find no evidence that imprisonment reduces the likelihood of recidivism. Instead, we find compelling evidence that offenders who are sentenced to prison have higher rates of recidivism and recidivate more quickly than do offenders placed on probation. We also find persuasive evidence that imprisonment has a more pronounced criminogenic effect on drug offenders than on other types of offenders.