The conclusions were obtained from the detailed survey of 1,285 students experiencing menstruation, who were chosen among 1,717 students in middle & high school girls in Seoul. The survey was conducted during July 20-July 24, 1971. 1. Age of Menarche An average age of menarche was 13.3$pm$1.07. The earliest age of menarche was 9 and the latest age 18. Ages of menarche were between 12 and 14 in 84.3 percent of the students surveyed. a. By present age distribution, the aged students were lower, than younger students in the average age of menarche. b. By father′s educational levels, among the students whose fathers were graduated from high schools, college & ever the earliest average age of menarche was found with 13.2, and among the students whose fathers were graduated from primary schools that wag latest with 13.6. c. By father′s occupations, among the students whose fathom engaged in "workers not classifiable"the earliest age of menarche was found with 12.5$pm$0.27, among the students whose fathers were in "service business"the second was 12.9$pm$1.07, and among the students whose fathers were in "miners, quarrymen and related workers"that was latest with 13.8$pm$1.14. d. By economic status, among the students of "wealthy"families the age of menarche was 13.1$pm$0.25, the among the students of "ordinary"families the lags of menarche 13.3$pm$1.06. and the among the students of "poor" families that was 13.8$pm$0.31. e. By home discipline, among the students being treated "rigid" the age of menarche was 13.5$pm$1.13, among the students being treated "moderate"the age of menarche was 13.3$pm$0.22, and those being treated "indifferent" that was 13.0$pm$0.26. f. By students physical condition, among the students of "good" condition the average of menarche was 13.3$pm$0.16, and among the students "poor" that was 13.5$pm$0.31. 2. Menstruation a. For the six months after the average of menarche 39.0 percent of the students had normal menstruations, and 61.3 percent of them had abnormal ones. Of the students with abnormal menstruation 21.7 percent had abnormal menstruation from time to time, 25.4 percent had no menstruation for one month to three months, 7.2 percent had menstruation for four to six months and 6.7 per cent had no menstruation for more than sin months. Most students became to have normal menstruations a few months later the age of menarche. b. At the time interviewed, the percentile of cycle of menstruation as following: 23 days types: 46.8 percent 30 days types: 40.6 percent others : 12.6 percent The average cycle of menstruation was every 28.9 days. c. The average duration of menstruation is 4.69 days. d. The subjective symptoms during menstruation period: Out of the total 89.7 per cent had some pains, while 10.3 percent had no symptom. Among the symptoms, abdominal pain occupied 29.9 percent, neurotic symptoms 19.0 percent and lumbago 15.1 percent. e. By attitude or Action at first physical change, "Treated it by own experience" : 30.0 percent "Don′t know what to do because of ignorance" : 20.1 percent "Asked others about it" : 43.0 percent