BACKGROUND: The prevalence of obesity was estimated based on self-reported height and weight recorded in the Community Health Survey (CHS), a nationwide survey which began in 2008. This study was conducted to evaluate the extent and consistency of underestimation in obesity and overweight prevalences in CHS compared to the Korea National Health and Nutrition Examination Survey (KNHANES) data. METHODS: In this study, we compared the prevalence estimates of obesity and overweight among Korean adults aged 20 and over using 2010 KNHANES and 2010 CHS data. In contrast to KNHANES data, where subjects' height and weight were actually measured, CHS data relied on subjects' self-reported height and weight. RESULTS: Compared to KNHANES, CHS underestimated the obesity and overweight prevalence by 8.6%P and 7.8%P, respectively. Height (men: -0.9 cm, women: -1.7 cm) was overestimated while weight (men: 0.5 kg, women: 1.1 kg) and body mass index (men: 0.4 kg/m2, women: 1.0 kg/m2) were underestimated in CHS compared to KNHANES data. The overestimation of height was greater as age increased and weight was underestimated by more than 1.0 kg among men aged 20~39 and women aged 20~49 according to CHS data. CONCLUSION: CHS underestimated both obesity and overweight prevalences among Korean adults and the degree of underestimation differed across gender and age.