To assess the prevalence of weight misperception in American adolescents and its association with diet and physical activity behaviors, "Youth Risk Behavior Survey" data were utilized for this study. Based on reported and perceived weight, adolescents in the study were grouped into four categories (true negative [52.4%] = normal body mass index [BMI]/accurate weight perception; false negative [11.3%] = high BMI/weight misperception; false positive [11.6%] = normal BMI/weight misperception; and true positive [24.8%] = high BMI/accurate weight perception). Diet and physical activity of adolescents were compared in these categories. A total of 12,016 participants were included in our analysis (74.9% aged 15-17 years, 54.5% Whites, 52% females). Almost a third (31.8%) were overweight and obese, and more than a fifth (22.9%) misperceived their weight (11.6% overestimated and 11.3% underestimated their weight). In a gender-stratified analysis, the odds of avoiding a healthy diet and physical inactivity were higher among those with body weight misperception.