Data from a survey of 200 Billings Ovulation Method acceptors in Korea were used to describe a profile of these natural family planning acceptors, and to calculate use effectiveness rates for twelve months of use among women using the method for avoiding an unplanned pregnancy. The majority of acceptors were women of proven fertility who wanted to limit their family size, and many of them (79%) had previously used a family planning method. Fifty-six percent were Catholics, and those study subjects were above middle income group by Korean annual household income estimates. The mean number of living children the NFP acceptors had was 2.3 ± 1.4 and the number of children they desired to have was 2.4 ± 1.4. The cumulative life table rate for unplanned pregnancies at the end of 12 months of use was 7 (± 2.5 S.E.) per 100 women, and women ever attending the learning sessions as couples experienced relatively less unplanned pregnancies compared to those women attending the sessions alone.