Background: The effects of diabetes mellitus (DM) on mortality and morbidities in burn patients have not been sufficiently elucidated. Objective: The present study aimed to investigate the effects of DM on the mortality, length of hospital stay, and number of operations in burn patients. Methods: A retrospective cohort study was performed using medical records of 3,220 burn patients. Multiple logistic regression, linear regression, and Poisson regression models were used to determine whether DM increases mortality in patients with burn injury, whether DM prolongs length of hospital stay in burn survivors, and whether DM increases the number of operations in burn survivors, respectively. Results: After adjusting for potential confounding factors, DM significantly increased odds of death in burn patients (adjusted odds ratio 3.225 [95% confidence interval 1.405∼7.400], p=0.006). DM also increased the mean length of hospital stay in burn survivors (adjusted mean ratio 1.312 [95% confidence interval 1.198∼1.437], p<0.001). Furthermore, DM significantly increased the mean number of operations in burn survivors (adjusted mean ratio 1.576 [95% confidence interval 1.391∼ 1.785], p<0.001). Conclusion: DM increases mortality, elongates hospital stay and makes more operations required in patients with burn injury. (Ann Dermatol 31(1) 51∼58, 2019