The persistent felony offender (PFO) statute that Kentucky adopted in 1974 is an example of a sentencing enhancement that targets career criminals. The objective of this law is to punish offenders for repeated criminal activity by charging them with a separate count of persistent criminal behavior. The law mandates that offenders sentenced under the PFO statute must serve 85 percent instead of 50 percent of their sentences prior to being eligible for parole. This study sought to determine whether the mandatory sentence lengths prescribed by the PFO statute were efficient. The study used a 1985 cohort of persistent felony offenders in Kentucky with at least one rape conviction (n=62), and it tracked recidivism rates up to 15 years later. Recidivism was defined as an additional incarceration due to either a new offense of any type or a parole violation. The ultimate purpose of the analysis was to determine the appropriate sentence length that would ensure offenders will remain trouble-free after release. The study used a survival analysis to determine the time to recidivism for each individual rapist. The study findings suggest a higher probability of not recidivating if the PFO rapists serve at least 20 percent of their sentence; however, no difference was found by 20 percent time served when the postrelease time period was extended to 85 percent of the sentence. Thus, lengthening the sentence of PFO rapists failed to prevent future offending. The 85-percent mandate of sentence served before parole eligibility serves only retributive aims, failing to produce a substantial incapacitation effect. These findings are consistent with other sex offender recidivism studies that have found less difference in reoffending as the length of the postrelease period increases. Only 9 out of 62 of the PFO rapists did not recidivate prior to 85 percent of their sentence expiring. The nine offenders who survived the longest after release were incarcerated for, at most, 66 percent of their sentences. 2 tables, 1 figure, and 57 references