Five candidate measures of psychological need-satisfaction were evaluated as predictors of high positive and low negative mood within the group, intrinsic motivation for group activities, and high commitment to the group. Consistent with self-determination theory (Deci & Ryan, 1991), personal autonomy and interpersonal relatedness both predicted positive outcomes. Consistent with optimal distinctiveness theory (Brewer, 1991), feeling included within the group, feeling personally distinctive within the group, and feeling that the group is distinctive compared to other groups, also predicted positive outcomes. Simultaneous regression analyses indicated that the five needs were differentially related to the different well-being indicators, and also suggested that group inclusion may be the most important need to satisfy within group contexts. Supplementary analyses showed that members of formal groups felt less personal autonomy, but more group distinctiveness, compared to informal group members.