A combination of genetic and environmental factors is thought to contribute to age of menarche. Adolescent athletes and dancers are much more likely to have a delayed menarche than are non-athletes. To examine the possible differential influence of heredity and environmental factors on menarcheal age, 350 adolescent dancers and non-dancers and their mothers were surveyed. The dancers had a later age of menarche than did the comparison group; their mothers did not differ with respect to menarcheal age, suggesting that delayed menarche in athletes is not solely due to genetic selection as inferred by maternal menarcheal age. Maternal menarcheal age was the best predictor of menarcheal age in the comparison sample, while leanness was in the dance sample.