Secondary amenorrhoea is found with increased incidence in female athletes performing hard endurance training, especially when combined with demands for a low body weight. The etiology is multifactorial, but the energy balance (energy intake) in relation to the amount and intensity of training probably plays a crucial role. Long-lasting amenorrhoea may reduce the bone mineral content, perhaps partly irreversibly, especially in the lumbar vertebrae in long-distance runners. In gymnasts and light-weight rowers with a similarly high incidence of amenorrhoea, a much less pronounced effect on the lumbar bone mineral content has been reported in a few, small studies, pointing to a possible positive influence of specific training. The finding of stress fractures in an amenorrhoeic athlete should lead to further evaluation of the bone mineral status.