Identification of the relationships between adolescent overweight and obesity and physical activity and a range of intrapersonal and interpersonal factors is necessary to develop relevant interventions which target the health needs of adolescents. This study examined adolescent body mass index (BMI) and participation in moderate and vigorous physical activity (MVPA) and their associations with school year, adolescent nutrition and sedentary behaviors, parent BMI, parent physical activity, and parent support adolescent physical activity. Participants included 295 adolescents and their parents. Logistic regression was used to examine associations between adolescent BMI, MVPA, and the range of adolescent and parent characteristics. Results indicated that parents and home environments play significant roles in the development and maintenance of adolescent overweight/obesity of physical activity behaviors. School-based interventions should ensure high levels of parent involvement and target male adolescents to reduce time spent in small screen recreation and female adolescents to increase participation in MVPA. (Contains 4 tables.)