Objective: To assess the effects of family structure and physical activity on late menarche. Research Methods and Procedures: Retrospectively ages at menarche, family sizes, birth orders and other variables were studied in 238 Congolese women including 90 premenarche - trained athletes, 18 post -menarche - trained athletes and 130 non-athletes. Results: Mean age at menarche was later (p<0.001) in pre-menarche (15.36+1.04 yrs) compared to post-menarche athletes (13.93+1.03 yrs) or to non-athletes (14.03+ 1.22 yrs), but similar (p>0.4) between these two last groups. Mean birth order or birth order within a family size was higher (p<0.01) in athletes than in non-athletes. Mean family size or sex ratio did not differ between groups. Controlling for the effectof duration of training before menarche abolished family size or birth order slight effect (p<0.05) on age at menarche, while the duration of training substantial effect (p<0.001) on age at menarche persisted after controlling for family size and birth order effects. Regression analysis confirmed that duration of training wasa better predictor of age at menarche than family size or birth order in pre-menarche athletes. Conclusion : Physical activity before puberty seems to be a more important determinant of late menarchethan family structure.