PIP: The influence of the Japanese superstition that females born in the year of Hinoe-Uma (Elder Fire Horse) possess undesirable characters and should not marry on the fertility of the Korean immigrant population in Japan was examined and compared with the influence of this superstition on the Japanese in Japan and the Korean population in Korea. The year of Hinoe-Uma occurs once in every 60 years according to the ancient Sino-Japanese almanac. For both the Koreans in Japan and the Japanese a remarkable drop in crude birthrates and a sharp increase in stillbirth rates was found for 1966. In contrast, Koreans in Korea showed only a steady decline in the crude birthrate. Clearly, the Japanese folk superstition played an important part in discouraging Koreans in Japan from having a child in 1966. The fact that no such effect was apparent among Koreans living in Korea suggests that this phenomenon is due to either the adoption or the mimicry of cultural practices on the part of the immigrant population.