Ages at menarche and selected menstrual characteristics in 204 nonathletes, 253 high school athletes, 386 college athletes, and 40 young top athletes of Japan were investigated by questionnaire. Data from the questionnaire have confirmed (a) the ascending trend of ages of menarche with advancement of training and competitive level, and (b) the diversity of mean age at menarche by sport in a given level. The menarcheal orders by sport in the literature have been found to be strikingly similar to those found in the present data. We offer the hypothesis that ages at menarche and selected menarcheal characteristics (a) are brought about by selection in the socialization process into sports participation, and (b) reflect the diversity of suitable physiques by sport. Also, the higher the training and competitive level, the more likely the occurrence of menstrual irregularity (cycle length and period duration) and/or dysmenorrhea (backache).