Previous evidence suggests that severe heat illness may cause permanent acute damage to the heart, kidneys, and liver, which may possibly lead to chronic and even fatal disorders. We investigated whether individuals who had been hospitalized for severe heat illness were at increased risk of cause-specific and total mortality. A cohort mortality study was conducted of male and female US Army personnel hospitalized for heat illness (HI) from 1971 to 2000 using appendicitis (APX) as the reference. Hospitalization records were acquired from the Total Army Injury and Health Outcomes Database (TAIHOD) for 3971 cases of HI and 17,233 APX reference cases. Subject vital status was established through the National Death Index. HI cases had a 40% increased risk of all-cause mortality compared to APX cases. Further examining cause-specific deaths, male cases of HI were at an increased rate of death from cardiovascular disease (CVD) (rate ratio (RR)=1.71, 95% confidence interval (CI): 1.01, 2.89) and ischemic heart disease (IHD) (RR=2.23, 95% CI: 1.02, 4.90) compared to APX reference cases. Our findings provide preliminary evidence for increased risk of mortality among those who have experienced prior hospitalization for heat illness.