Little is known about the correlates of physical activity and sedentary behavior in Hispanic adolescents. This study examined at baseline and 2-year follow-up: (1) the relationship between self-efficacy for physical activity and physical activity, (2) the association of weight perception with physical activity and sedentary behavior, and (3) whether sex moderated these associations. Hispanic adolescents (N = 483 at baseline; age 15-17 years; 55.1% girls) completed questionnaires that assessed their self-efficacy for physical activity, weight perception, and time spent in physical activity and sedentary behavior. Multiple-group path analyses were conducted to examine the proposed relationships and determine whether they were moderated by sex. Models controlled for body mass index, weight loss intention, participation on a sports team, language spoken at home, parental education, and country of birth. Self-efficacy was related to time spent in physical activity in boys (b = 0.35, p < 0.001) and girls (b = 0.41, p < 0.001) at baseline, but not 2 years later. No association was found for weight perception and time spent in physical activity and sedentary behavior. Post hoc analyses for overweight participants at baseline showed that weight perception was associated with time spent watching television. Overall, the findings suggest that self-efficacy is an important correlate, but not a predictor, of physical activity among Hispanic adolescents. Including strategies to address and enhance self-efficacy for physical activity in lifestyle interventions may increase adherence to physical activity recommendations and help reduce the high prevalence of obesity in this population.