Sulfur mustard has been employed in chemical warfare in certain regions including Iran. The short and long term biological effects of sulfur mustard contamination have been studied in both basic and clinical aspects. Sulfur mustard has been shown to induce a vast array of pathological effects in affected persons. In addition to skin, lung, eyes and gastrointestinal disturbances, sulfur mustard has been shown to induce hematological complications and a severe suppression of the immune system. The short and long term immunological (both cellular and humoral), hematological, genetic and biochemical consequences of persons exposed to sulfur mustard are extensively reviewed here. The long term complications of these patients indicate the need to develop effective preventive and therapeutic strategies in the clinic. These strategies may be based upon immunopotentiating intervention and therapy.