Objectives: The purposes of this study were to examine the associations of social relationships with teachers and peers (i.e., peer acceptance, presence of a best friend and close friends, teacher support) to SPA in physical education and to test the mediating role of motivation regulations in the relationship between social physique anxiety (SPA; Hart, Leary, & Rejeski, 1989) and behavior (i.e., effort, participation avoidance). Design: Cross-sectional survey. Method: High school physical education students (N = 146; M-age = 15.9 years) completed an online survey in their school's computer lab assessing study variables. Results: Results of a hierarchical multiple regression analysis revealed that perceived peer acceptance was a negative predictor (p < .01) of SPA. In addition, path analysis did not support the mediating role of individual motivation regulations in the relationship between SPA and behavior. Results of the path analysis showed SPA as a negative predictor of autonomous motivation and a positive predictor of external regulation, amotivation and participation avoidance. Finally, students with greater autonomous motivation and introjected regulation and lower amotivation reported more effort in class and greater amotivation predicted a higher likelihood of avoiding participation in class. Conclusions: General feelings of acceptance and belonging among one's peers may help buffer against feelings of SPA in physical education. In addition, SPA demonstrates different relationships with individual motivation regulations and behavior in this setting. However, the lack of support for the mediating roles of individual motivation regulations suggests a more complex relationship among SPA, motivation and behavior and requires further testing. (C)2011 Elsevier Ltd. All rights reserved.