The purpose of this survey was to obtain information on the prevalence, costs, and patterns of use of complementary and alternative medicine (CAM) in a general population in the Republic of Korea. In 2006, we conducted nationwide and population-weighted personal interviews with 6,021 adults ranging from 30 to 69 yr of age; the final sample consisted of 3,000 people with a 49.8% response rate. In addition to their general socio-demographics, the respondents were asked about their use of CAM during the previous 12-month period, costs, sources of information, and reasons for use. The prevalence of use overall was 74.8%, while biologically based CAM therapies were the most likely type of use (65.4%). The median annual out-of-pocket expenditures for CAM therapies was about US$203. The primary reason for using CAM was for disease prevention and health promotion (78.8%). The main source of advice about CAM therapies use was most likely to be from family and friends (66.9%). Our study suggests that CAM use has been and continues to be very popular in South Korea. Conventional western medical doctors and governments should obtain more evidence and become more interested in CAM therapies.