The life expectancy of persons cycling through the prison system is unknown. The authors sought to determine the 15.5-year survival of 23,510 persons imprisoned in the state of Georgia on June 30, 1991. After linking prison and mortality records, they calculated standardized mortality ratios (SMRs). The cohort experienced 2,650 deaths during follow-up, which were 799 more than expected (SMR = 1.43, 95% confidence interval (CI): 1.38, 1.49). Mortality during incarceration was low (SMR = 0.85, 95% CI: 0.77, 0.94), while postrelease mortality was high (SMR = 1.54, 95% CI: 1.48, 1.61). SMRs varied by race, with black men exhibiting lower relative mortality than white men. Black men were the only demographic subgroup to experience significantly lower mortality while incarcerated (SMR = 0.66, 95% CI: 0.58, 0.76), while white men experienced elevated mortality while incarcerated (SMR = 1.28, 95% CI: 1.10, 1.48). Four causes of death (homicide, transportation, accidental poisoning, and suicide) accounted for 74% of the decreased mortality during incarceration, while 6 causes (human immunodeficiency virus infection, cancer, cirrhosis, homicide, transportation, and accidental poisoning) accounted for 62% of the excess mortality following release. Adjustment for compassionate releases eliminated the protective effect of incarceration on mortality. These results suggest that the low mortality inside prisons can be explained by the rarity of deaths unlikely to occur in the context of incarceration and compassionate releases of moribund patients.