The purpose of this study was to examine the influence of the gravitation of the Moon on the frequency of births in Kyoto, Japan. A retrospective cohort analysis of 1007 consecutive births without the use of the induction agents was conducted on a population of births in a private midwife hospital from January, 1966 to December, 2000. There was a significant increase in the cases of births, when the gravitation of the Moon to the Earth was less than 31.5 N. Results of this study suggest that the gravitation of the Moon has an influence on the frequency of births.