PURPOSE: The aim of this study was to determine, using prenatal ultrasongraphy, normal fetal foot length and the femur length ratio during the second trimester of a normal pregnancy in Korean women. MATERIALS AND METHODS: From May to July 1999, and in September of the same year, 1018 normal Korean singleton pregnancies showing no abnormality on prenatal sonograms were included in this study. The gestational age ranged from 19 to 30 weeks. Femur and foot length were measured by one radiologist. Regression analysis was performed for foot length and gestational age, and the mean value of the femur/foot length ratio and 95th percentile confidence interval of that mean value were calculated. The data obtained was compared with that obtained from caucasians. RESULTS: Foot length correlated with gestational age (r 2=0.87, p value = 0.0001). The regression formula was as follows; Gestational age (days) = 70.98-2.15 x foot length (mm). Mean foot length at each gestational week was not different from the corresponding figure for Cancasians. The mean (+/-SD) value of the femur/foot length ratio was 0.96 (+/-0.05) and the 95th percentile confidence interval of that mean value was 0.96+/-0.000301, figures which are significantly lower than those for Caucasians. CONCLUSION: Fetal foot length during the second trimester of a normal pregnancy in Korean women is a reliable parameter for use in the assessment of gestational age. In our study the fetal foot length was not different from that of caucasians, while the femur/foot length ratio was lower than the value in that group. The nomogram depicted in of this study will serve as a useful adjunct in the screening of chromosomal abnormality or skeletal dysplasia among Koreans.