The prevalence of obesity is increasing. In Korea, this is especially true of men in general, and women of low socioeconomic status. Misperception of body weight poses a barrier to the prevention of obesity. In this study, the misperception of body weight in relation to actual body weight and associated factors in Korean adults was evaluated. Data from 7162 adults who participated in the 2009 Korean National Health and Nutrition Examination Survey were analyzed. Misperception of body weight was substantial in Koreans, with 48.9% underestimating and 6.8% overestimating their weight status. More men than women underestimated their weight status. Weight perception in women was affected more by sociodemographic characteristics. Women's underestimation was positively associated with older age, marital status, and lower socioeconomic status. This suggests that increasing public awareness of healthy weight will be helpful to counteract the current obesity epidemic in Korea.