Early research has shown that leadership behaviour is viewed as a crucial factor in successfully developing team cohesion, effectively resulting in greater team satisfaction and more positive team outcomes. However, little is understood if these same factors have an impact on physical activity groups. Objective: The purpose of this study was to investigate the relationship between leader behaviours and group cohesiveness within women's physical activity groups. Design: Participants (N=95) included a sub-sample of adult women who were previously involved in a women's physical activity/walking program. Methods: Participants assessed their groups' leader behaviour using items pertaining to enthusiasm, motivation, instruction and availability, and their groups' cohesiveness using the Physical Activity Group Environment Questionnaire (PAGEQ). Canonical correlation analysis was used to determine the strength of association between the four concepts of group cohesion (ATG-T, ATG-S, GI-T & GI-S) and the four items pertaining to leadership behaviour. Results: A significant multivariate relationship was revealed between group cohesion and leadership behaviour, Wilks' lambda=0.43, F(16,170)=5.16, p<0.001. The canonical correlation for this function was RC=0.74, indicating a strong relationship. Simply stated, group leaders who were perceived as being highly enthusiastic, who have a high ability to motivate, who have a high ability to provide personal instruction and who are available outside of the group's regular activities were associated with higher levels of group cohesion. Conclusions: Although a cause-effect relationship can not be determined, the current study can serve as a valuable template in guiding future research in examining potential mechanisms that may assist with physical activity sustainability.