Document Type



The age at menarche of 284 school girls born and raised in urban districts was investigated. The arithmetic mean was 12.40 years and the range was from 9.63 to 15.44 years. Mean menarchial ages reported in Japan from 1884 to 1980 were gathered and the course of the secular change during the last 100 years was examined using regression techniques. The decrease in age was slow and constant before the war, but fast at first and then slow after the war. The secular changes in peak height velocity were shown to be similar to those of menarche.