To assess the effects of family structure and physical activity on late menarche,retrospectively ages at menarche, family sizes, birth orders and other variableswere studied in 238 Congolese women including 90 pre-menarche-trainedathletes, 18 post menarche-trained athletes and 130 non-athletes.Mean age at menarche was later (p,.001) in pre-menarche (15.3661.04yrs) compared to post menarche athletes (13.9361.03 yrs) or to non-athletes(14.0361.22 yrs), but similar (p..4) between these two last groups. Mean birthorder or birth order within a family size was higher (p,.01) in athletes than innon-athletes. Mean family size or sex ratio did not differ between groups.Controlling for the effect of duration of training before menarche abolished family size or birth order slight effect (p,.05) on age at menarche, while theduration of training substantial effect (p,.001) on age at menarche persistedafter controlling for family size and birth order effects. Regression analysisconfirmed that duration of training was a better predictor of age at menarche thanfamily size or birth order in pre-menarche athletes. In conclusion, physicalactivity before puberty seems to be a more important determinant of latemenarche than family structure.