Heat stress is an occupational health problem affecting Man in diverse, hostile environments ranging from deep mining to outer space. Healthy, young military recruits and industrial workers exposed to hot, humid environments are typically at risk. The International Classification of Diseases classifies heat disorders into 10 separate entities, of which the most clinically significant are heat cramps, heat exhaustion and heat stroke. The latter is a medical emergency of the first order. Clinical management hinges upon early treatment based on a high index of suspicion. Effective preventive measures and adequate education of those at risk form the basis for its control.