OBJECTIVES: To examine the prevalence of the use of complementary and alternative medicine (CAM) in the Republic of Korea and identify the factors responsible for variations in the reported prevalence, the socio-demographic factors associated with CAM use, and the relationship between CAM use and study methodological quality. DESIGN: Two international and 6 representative Korean medical databases were searched to identify cross-sectional studies that had surveyed the general Korean population in community settings to determine prevalence of CAM use. Data collection and assessment of the methodological quality of the studies were conducted by 3 independent reviewers. RESULTS: The prevalence of CAM use reported by the 11 studies that met the selection criteria ranged from 29% to 83%. Inclusion of Korean medicine within the definition of CAM was not found to be a significant factor in the heterogeneity, but several factors that may have contributed to it, namely, inconsistency in CAM taxonomies, recall bias, use of unrepresentative sampling strategies, and lack of pilot testing, were identified. Higher CAM use was found to be associated with female sex, high level of education, and advanced age. CONCLUSIONS: The inclusion of Korean medicine within the definition of CAM does not explain the heterogeneity in the reported prevalence of CAM use among the South Korean population. A standard questionnaire appropriate for the Korean context should be developed to define and classify the common CAM modalities and control for confounding factors.