In a survey of 75 dancers (mean age, 24.3 years) in four professional ballet companies, we found that the prevalence of scoliosis was 24 percent and that it rose with increases in age at menarche. Fifteen of 18 dancers (83 percent) with scoliosis had had a delayed menarche (14 years or older), as compared with 31 of 57 dancers (54 percent) without scoliosis (P less than 0.04). The dancers with scoliosis had a slightly higher prevalence of secondary amenorrhea (44 percent vs. 31 percent), the mean (+/- SD) duration of their amenorrhea was longer (11.4 +/- 18.3 vs. 4.1 +/- 7.4 months; P less than 0.05), and they scored higher on a questionnaire that assessed anorectic behavior. The incidence of fractures was 61 percent (46 of 75 dancers), and it rose with increasing age at menarche. Sixty-nine percent of the fractures that were described were stress fractures (mostly in the metatarsals), and their occurrence had an even stronger correlation with increased age at menarche. The incidence of secondary amenorrhea was twice as high among the dancers with stress fractures (P less than 0.01), and its duration was longer (P less than 0.05). In 7 of 10 dancers in whom endocrine studies were performed, the amenorrheic intervals were marked by prolonged hypoestrogenism. These data suggest that a delay in menarche and prolonged intervals of amenorrhea that reflect prolonged hypoestrogenism may predispose ballet dancers to scoliosis and stress fractures.