Background Suicide is a leading cause of death in South Korea (hereafter ‘Korea’), and there is evidence that body weight and perceived weight affecting suicide have a significant effect on suicidal behavior in adolescence. This study investigated the association between body mass index (BMI), perceived weight, and suicide attempts in adolescents. Methods We included nationally representative data for a total of 106,320 students in our final analysis. We calculated and stratified BMI (underweight, normal weight, overweight) to determine the correlation between BMI and suicide attempts. We stratified the participants into three groups (perceived as underweight, normal weight, and overweight) for subjective body weight perception to analyze the relationship between subjective body weight perception and suicide attempts. We further analyzed the combination of BMI and subjective body weight perception to determine the relationship between suicide attempts and distorted subjective weight perception. Results Compared with perceiving oneself as having a normal weight, the odds ratios (ORs) for suicide attempts were significantly increased in the group perceiving themselves as overweight. In addition, those who perceived themselves as overweight but were underweight according to their BMI were at significantly increased risk of suicide attempts relative to those who perceived themselves as about the right weight. Conclusions There was a significant association with suicide attempts in the underweight and perceived overweight group. This shows the importance of combining BMI and perceived weight when examining the relationship between weight and suicide attempts in adolescents.