Background: To improve understanding of the mechanisms affecting the relationship between adolescent obesity and poor academic performance, we examined the association of overweight or perceived weight status with academic achievement. Methods: We performed a cross-sectional study of 14-17-year-olds (N = 11,012) from the nationally representative 2003 Youth Risk Behavior Survey. The main outcome measure was self-reported grades (mostly A, B, C, D, or F). The primary independent variables were medically defined overweight (body mass index [BMI] [greater than or equal to] 85th percentile), obesity (BMI [greater than or equal to] 95th percentile), and participants' perception of their weight status. Results: Medically defined overweight youth were less likely to report higher grades in unadjusted analysis (OR 0.67, 95% CI: 0.60-0.76, p less than 0.001) and after adjustment for demographics, depression, television and video game use, and physical activity (OR 0.83, 95% CI: 0.74-0.94, p = 0.003). Statistically significant results also were seen with medically defined obese participants. Youth who perceived themselves as overweight were less likely to report higher grades (OR 0.82, 95% CI: 0.73-0.92, p = 0.001) in unadjusted analysis and after adjustment for the same variables (OR 0.79, 95% CI: 0.68-0.91, p = 0.002). The perception of overweight was a more significant determinant of academic performance (OR 0.81, 95% CI: 0.69-0.95, p = 0.012) compared to medically defined obesity (OR 0.90, 95% CI: 0.77-1.05, p = 0.174). Conclusions: Perceived overweight status is negatively associated with academic performance, regardless of actual weight status. These findings suggest that perception of overweight may be a mechanism for prior results indicating a negative association of obesity and academic achievements, and have implications for the academic health of these adolescents. (Contains 3 tables and 1 figure.)