Recent studies have examined the prevalence of disordered eating and other health risk behaviors among adolescent boys and girls. However, these studies generally have not examined predictors of these behaviors, and have not embedded the investigations within a theoretical framework. This study employed a longitudinal design to evaluate the validity of a biosocial model in explaining health risk behaviors related to extreme body change strategies (disordered eating, exercise dependence, use of food supplements, steroid use) among adolescents. The participants were 430 adolescent boys (mean age = 13.33 years) and 451 adolescent girls (mean age = 13.28 years) who completed measures of pubertal timing, perceived popularity with peers, body dissatisfaction, focus on sport, involvement in competitive sport, strategies to lose weight, strategies to increase muscle, disordered eating, use of food supplements and steroids, and exercise dependence. It was found that both early and late maturing girls were at greatest risk of engaging in health risk behaviors, whereas boys demonstrated more variability in the relationship between pubertal timing and extreme body change behaviors. The results of this study provide important insights into the role of pubertal development in the adoption of extreme body change behaviors among adolescents. (Includes Tables and Bibliography.)