Sulphur mustard is a chemical warfare agent, which was largely used during the World War One and in Iraq-Iran conflict. It may also be used as a chemical terrorism agent. Therefore, medical professions should have sufficient knowledge and be prepared for medical intervention of any such chemical attack.Sulphur mustard exerts direct toxic effects on the eyes, skin, and respiratory tract, with subsequent systemic actions on the nervous, immunologic, hematologic, digestive, and reproductive systems. It is an alkylating agent that affects DNA synthesis and thus, delayed complications have been considered since the World War One. Cases of malignancies in the target organs particularly in hematopoietic, respiratory, and digestive systems were reported. Common delayed respiratory complications include chronic bronchitis, bronchiectasis, frequent bronchopneumonia, and pulmonary fibrosis, all of which tend to deteriorate with time. Severe dry skin, delayed keratitis, and reduction of natural killer cells with subsequent increased risk of infections and malignancies are also among the most distressing long-term consequences of sulphur mustard intoxication. However, despite extensive research that has been conducted on Iranian veterans during the past decades, major gaps continue to remain in the sulphur mustard literature. Immunological and neurological dysfunctions and the relationship between exposure to sulphur mustard and mutagenicity, carcinogenicity, and teratogenicity are important fields that require further studies, particularly on Iranian veterans with chronic health problems caused by sulphur mustard poisoning. There is also a paucity of information on the medical management of acute and delayed toxic effects of sulphur mustard poisoning, a subject that greatly challenges the medical professions.