This study examines relationships among weight status, weight perceptions, and dieting behaviors in South Korean adolescents. As perceptions of an ideal body for teens in Korea have changed over time, it is important for school nurses to understand these relationships to help students achieve health. A cross-sectional survey of 3,191 8th and 2,252 11th-grade students from 21 middle and high schools across Korea completed a self-administered questionnaire. The prevalence of overweight among adolescents was 17.5% in males and 6.0% in females. Overall, 65.9% of students perceived their weight status accurately. Females overestimated their weight status 2.3 times more often than males. Male students underestimated their weight status 2.7 times more frequently than females. Approximately one third of participants misperceived their weight status, with variations existing between males and females. Study results suggest the need to develop male- and female-specific interventions to promote healthy body images and body weight.