Two independent studies were conducted to examine the impact of group size in an exercise setting. In the first, archival data from 47 exercise classes varying in size from 5 to 46 members were used to examine the relationship between group size and behavior. Attention and retention were high in small and large exercise classes and specific social psychologocal correlates of group size including the participants’ perceptions of conspicuousness, quality and quantity of interactions with their leader, their opportunities for social interaction with other members, the level of crowding and density, and satisfaction. Trend analyses showed a curvilinear relationship between exercise class size and participants’ perceptions of the opportunities available for social interaction and feelings of crowding and density. Both the small and large classes were perceived more favorably than the medium classes. The relationships between class size and perceptions of the instructor as well as the level of satisfaction experienced were linear—positive perceptions decreased systematically as class size increased.