BACKGROUND: To examine the associations and differences between gender and weight classification for physical activity (PA) and individual, social, and parental factors. METHODS: Data from wave 2 of the Growing up in Ireland" national study were used, resulting in a sample of 7525 13-year-old adolescents. Information on factors affecting adolescents' social, emotional, cognitive, and physical development was collected. RESULTS: Overweight (OW) adolescents were more likely to exercise and restrict food for weight loss and less likely to perform moderate to vigorous PA than normal weight adolescents. Parent body mass index was associated with adolescent body mass index for OW and normal weight adolescents, with the strongest association seen with OW females. Parents of OW adolescents considered themselves to be more OW and less physically active than parents of normal weight adolescents. Furthermore, for all groups, a greater amount of moderate to vigorous PA was associated with less television viewing, greater PA of parents, and a greater number of friends. CONCLUSION: Parental health behaviors play a significant role in adolescents' bodyweight, representing the necessity for more constructive health behaviors and PA among parents. Future interventions may be strengthened by focusing specifically on gender and body mass index, while taking into consideration the importance of parental behaviors on adolescents."