A prospective study of the menstrual pattern and weight changes was made in the first year of training of 29 new female entrants to a professional ballet school. Seventy-nine per cent of the student girls had menstrual disturbances at entry: primary amenorrhoea, four; secondary amenorrhoea, 11; irregular menses, eight. The incidence of secondary amenorrhoea increase substantially by the end of the year (20), but was not associated with any significant change in body weight. Only three students menstruated regularly during the year. Menstrual regularity improved during periods of injury and long vacation and it appears that deterioration of the menstrual pattern during dancing periods was related to strenuous physical exercise rather than to any change in body weight.