The general principle that the experience of combat damages servicemen's long-term physical and mental health is recognized. However, controversy has raged over the nature of particular post-combat disorders such as shell shock, disordered action of the heart (DAH), effort syndrome, effects of Agent Orange and, not least, Gulf War syndrome. We, among many others, have argued that they should be classified as functional syndromes characterized by medically unexplained symptoms, which include: fatigue, weakness, sleep difficulties, headache, muscle ache and joint pain, problems with memory, attention and concentration, nausea and other gastro-intestinal symptoms, anxiety, depression, irritability, palpitations, shortness of breath, dizziness, sore throat and dry mouth. Despite popular claims to the contrary, no simple biomedical aetiology has been discovered to account for these disorders, hence the term “medically unexplained”. Furthermore, they are not easily interpreted using accepted psychiatric classifications. Without demonstrable organic cause, war syndromes have attracted diverse causal explanations, ranging from pressure on the arteries of the chest, constitutional inferiority, toxic exposure, bacterial infection to microscopic cerebral haemorrhage.