Classically, sports activities are thought to have a beneficial effect on bone tissues. Actually, there are many interactions between sports activities and bone tissue and in certain cases complex hormone disorders may develop. Recent progress in the evaluation of bone structure (absorptiometry) and better understanding of the neuroendocrine functions have improved our knowledge of these interactions and helped provide answers as to the true effect of sports, and particular high-level training, on bone tissue. Mechanical stimulation of bone increases the level of both cortical and cancellous bone formation. The mechanical effect is localized in areas under particular constraint such as the lower limbs in runners and the upper predominant limb in tennis players. Inversely, hypoestrogenism, similar to anorexia nervosa, has been observed to be the cause of general bone loss and increased risk of osteoporosis in certain high level athletes. When these two opposing phenomena occur simultaneously, there is generally an overall loss of cancellous bone mass while bones submitted to major mechanical stress may be relatively protected. Amenorrhoea, particularly in long distance runners, generally occurs when training exceeds 30 km per week. Menarche may be delayed by 1 or 2 years when training begins early and dismenorrhoea is seen in 50% or more of the athletes. Amenorrhoea results from a central disorder due to insufficient pulsatile secretion of luteo-releasing hormone and subsequent hypogonadism. The role of beta-endorphins or catelestrogens on hypothalamic receptors has been suggested as the underlying mechanism. These different observations help provide answers to the different problems raised when providing counselling and care for high level athletes.