Background: Mustard gas is a disabling chemical weapon and was widely used in first world war and Iraq-Iran war. Its toxic effects could be acute or chronic and they could particularly affects lungs, eyes and skin. Objective: To study the frequency of chronic complications of sulfure Mustard gas in Iranian victims 14 to 20 years after exposure. Patients and Methods: This descriptive cross-sectional study was performed on 800 patients that were randomly selected from different provinces of Iran, who had been exposed to sulfure Mustard gas during 1983 to 1988. These patients were clinically re-evaluated in 2002-03 and laboratory tests were performed if necessary. Results: The mean age of the patients at the time of study was 39.3 (±9.8) years. 3 types of skin lesions were observed. Non-specific lesions including 39.6% xerosis, 19% pigmentary disorders, 17.4% cherry angioma, 12.7% seborrheic dermatitis, 12.2% eczema (Dermatitis), 11.6% acneiform lesions, 7% tinea versicolor, 5.1% urticaria, 3.6% vitiligo, 2.5% alopecia areata, 2% psoriasis, and 1.3% aphthous stomatitis. Specific skin lesion called mustard scar was defined according to morphology, location, history and observed in 44 (5.5%) patients. Malignant neoplasms including basal cell carcinoma, Bowen’s disease, squamous cell carcinoma, mycosis fungoides and dermatofibrosarcoma protuberans occurred in 9 victims (1.1%). Conclusion: Mustard gas can cause acute and late-onset skin lesions. Specific lesion of Mustard gas called Mustard scar is the most important finding of this study.