Background: This study examined the mediating function of body weight perception (BWP) in the relation between body mass index (BMI) and unhealthy weight control behaviors (UWCBs; eg, fasting, using diet pills, or laxatives), and between BMI and suicidal ideation. It also explored the correlation between exposure to multiple UWCBs and suicidal ideation among Korean adolescents. Methods: Data on BMI, BWP, UWCBs, and suicidal ideation were obtained from the 2006 Korean Youth Risk Behavior Web-based Survey, a school-based survey conducted on a nationally representative sample of students in grades 7-12 (36,463 boys and 33,433 girls). Data were analyzed using bivariate and multivariate logistic regression. Results: BMI was significantly associated with both UWCB and suicidal ideation among boys and girls, even after controlling for covariates. However, the significance and magnitude of the association between BMI and UWCB were considerably attenuated when BWP was added to the model. When BWP was included, the association between overweight BMI status and suicidal ideation became nonsignificant in both sexes, whereas the association between underweight BMI status and suicidal ideation remained significant among boys. Adolescent boys and girls engaging in multiple UWCBs were at greater risk for experiencing suicidal thoughts. Conclusions: This study suggests that BWP represents a potential mediator between BMI and UWCB, and between BMI and suicidal ideation among both boys and girls. Thus, school programs addressing issues related to BWP should be developed and targeted at adolescents to reduce the potential risks for both UWCB and suicidal behavior. (Contains 4 tables and 1 figure.)