There is a popular belief that physical fitness and mental stability are related. In this article, Mike Sheehan reviews the history of sport in psychiatric nursing, establishes the theories behind using sport as an adjunctive therapy, explores the concepts of using sport as a specifically prescribed treatment and investigates the advantages which are available when using individual sports in conjunction with existing treatment options. He has looked at three main areas of psychiatric illness: schizophrenia, depression and anxiety disorders. The ‘exercise prescription' required in all three illnesses differs as much as the symptoms experienced by those who suffer from the conditions. The use of exercise intervention in the prevention and treatment of psychological illness is relatively safe, inexpensive and invokes no adverse side-effects. The role of the sports therapist, based on unique skills and knowledge, is described.