Twenty-two female teenagers engaged in elite gymnast training were prospectively studied during a five-year period and their pubertal development was recorded. Height and weight, as well as stage of development according to Tanner, were registered every six months. FSH, LH, TSH and prolactin were measured in girls who had not yet had their first menstrual period. Twenty-two healthy school girls in the same age group who were not actively engaged in physical exercise served as a control group. Pubertal development was completed during the observation period in all the gymnasts but one, who had primary amenorrhea at the age of eighteen. As a group, the gymnasts had a significantly delayed age of menarche compared to the control group and to normal Swedish girls. They also had significantly less body fat and were shorter and lighter than the control group. They grew much more slowly and did not have the distinct growth spurt seen in the controls. The final height of six of the gymnasts was less than the expected height. The frequency of injuries was high in the gymnasts, which might be a result of hard training combined with late menarche and low body fat.