This study tested a structural equation model to estimate the relationship between health behaviors, body mass index (BMI), and self-esteem and the academic achievement of adolescents. The authors analyzed survey data from the 2000 study of "Youth in Iceland", a population-based, cross-sectional sample of 6,346 adolescents in Iceland. The model demonstrated good fit with chi-square of 2685 (n = 5,810, df = 180), p less than 0.001, Comparative Fit Index value of 0.94, and a root mean square error of approximation of 0.049. Lower BMI, physical activity, and good dietary habits were all associated with higher academic achievement; however, health behavior was positively and robustly associated with greater self-esteem. Self-esteem was positively influenced both through physical activity ([beta] = 0.16) and the consumption of fruits and vegetables ([beta] = 0.14). In contrast, poor dietary habits negatively influenced self-esteem and academic achievement, and self-esteem was negatively influenced by increasing levels of BMI ([beta] = -0.05). (Contains 2 tables and 1 figure.)