Objective: The objective was to examine a breadth of personal, behavioral, and socio-environmental factors as potential risk and protective factors of overweight among male and female adolescents. Research Methods and Procedures: A longitudinal study was conducted with an ethnically and socio-economically diverse sample of 2516 adolescents who completed surveys at both Time 1 (1998 to 1999) and Time 2 (2003 to 2004) of the Project Eating Among Teens (EAT) study. Results: In 1998 to 1999, 335 (25.7%) girls and 282 (26.4%) boys met the age-adjusted criteria for overweight. During the 5-year study period, 236 (70.5%) of the overweight girls and 185 (65.7%) of the overweight boys remained overweight and 115 (12.0%) girls and 77 (9.9%) boys originally not overweight became overweight. Although differences by sex were found, a number of personal, behavioral, and socio-environmental factors were associated with overweight among both male and female adolescents. Body dissatisfaction and weight concerns at Time 1 predicted overweight at Time 2 for both male and female adolescents. Dieting and use of unhealthy weight control behaviors at Time 1 also predicted overweight at Time 2. Greater frequency of breakfast consumption at Time 1 was protective against overweight. Higher levels of weight-related teasing and parental weight-related concerns and behaviors at Time 1 were positively associated with Time 2 overweight. Discussion: Body dissatisfaction, weight concerns, use of unhealthy weight control behaviors, weight-related stigmatization, and parental concern about the child's weight may increase risk for adolescent overweight. Interventions that enhance adolescents' body satisfaction while providing them with skills to avoid dieting and to engage in more effective weight-control behaviors should be developed and tested.