The purpose of this study was to examine how attitude, subjective norm, and perceived behavioral control influence adolescents' intent to participate in active family leisure and furthermore to explore the nature of the relationship between active family leisure and body mass index (BMI) among adolescents. Adolescents (N = 472) completed an online questionnaire assessing the theory of planned behavior (TPB) variables, active family leisure, individual active leisure, and BMI. Structural equation modeling was used to analyze the data. Tests of direct paths of attitude, subjective norm, and perceived behavioral control to intent indicated these variables were significant predictors of intent to participate in active family leisure. The combination of attitude and subjective norm was the greatest predictor of intent. The TPB was extended to examine the relationship between active family leisure and BMI. There was not a significant relationship; however the TPB did accurately model the behavior of active family leisure. Findings suggest the influence of friends and family is a strong predictor for active family leisure. This highlights the important role families and friends can play to encourage adolescents' participation in active family leisure.