Lung exposure to sulfur mustard (SM) results in pulmonary complications, which is the main cause of long-term disability and morbidity. Up to now, the precise mechanisms of SM-induced lung complications has not been identified. The aim of this study was to evaluate apoptosis in the lung tissue of SM-exposed individuals. The study was performed on archived lung paraffin-embedded tissue specimens of21 patients suffering from pulmonary complications due to previous SM exposure and 9 unexposed patients who had undergone lung resections for another lung disease. Evaluation of apoptosis in paraffin-embedded lung tissue sections was performed using terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) assay and the cleaved caspase-3 immunohistochemistry assays. TUNEL-positive apoptotic features and caspase-3 expression of specimens were significantly higher in the SM-exposed group compared with the control group. This result demonstrates higher apoptosis rate in the SM-exposed group. Furthermore, the majority of positive cells consisted of alveolar epithelial cells in both methods. In conclusion,it seems that exposure to SM may result in increased apoptosis in respiratory epithelium. More studies are needed to evaluate the role of apoptosis in SM-induced lung complications in order to design new and effective therapeutic protocols.