The present study examines the Korean sex ratio at birth using Vital Statistics Korea data from 1970 to 1998. Since 1980, in most years, the sex ratio at birth correlated positively with the birth order (p<0.05). The results demonstrate that the ratio has dramatically increased in the past two decades, especially for higher birth orders, with the ratio reaching a maximum of 224.7 and 202.8 in 1994 at the third and fourth birth orders, respectively . Korean society has traditionally held a strong preference for having sons. In the mid-1980s, advanced medical technology for sex predetermination and sex preselection became popular and enabled mothers to try to choose the sex of the baby. The increased sex ratio at birth at higher birth orders is presumably attributed to the technological advances . As a result, the Korean government introduced laws to prohibit using such medical technology . Other factors affecting the recent trends of sex ratio at birth are also discussed, including Korean culture and social trends such as the decline in fertility.