[Secular change in the seasonal distribution of menarche in Tokyo].

Secular change in the seasonal distribution of menarche was studied in Tokyo on 17545 females born during 1881 - 1963. The distribution in those born before 1890 showed peak (March-May) and a wide trough during July-October. Occurrences of menarche came to concentrate in April and August after 1890, and also in January after 1950. The distributional pattern has much changed by the period of birth year.