Objectives: To investigate the determinants of mortality and the lethal area 50 (LA50) in large series of Iranian burn patients admitted to a single burn center.Methods: This cross-sectional study was conducted in Shahid Motahari burn center of Tehran, Iran during a 1-year period from 2011 to 2012. We included all the burn patients who were admitted to our center during the study period. Those with incomplete medical records and those referred to other centers were excluded from the study. The medical records of the included patients were reviewed and the demographic, clinical, laboratory and outcome measures were recorded. The mortality rate was recorded and the determinants of LA50 were analyzed in a univariate and stepwise multivariate model.Result: Overall we included a total number of 1200 subjects with mean age of 30.8 ±18 years. There were 907 (75.6%) men and 293 (24.4%) women among the patients. The total LA50 was 55.5% (95% CI: 52.98%-58.3 %). There was a significant difference between age group >61 years and two 11-20 and 21-30 groups regarding LA50. The advanced age (p<0.001), female gender (p=0.002), inhalational injury (p<0.001) and burn extension determined by TBSA% (p<0.001) were significantly associated with mortality. In addition, male gender (p=0.087), flame (p=0.156), scald (p=0.088) and chemical injuries (p=0.071) were not associated with mortality.Conclusion: The LA50 determine din our study is still much lower than that reported in developed countries, as a result, the quality of medical care is lower. Female gender, age, inhalational injury and extension of burn determined by TBSA% were found to be the independent risk factors of mortality in burn patients in our series.