Expertise assignment has been proposed to improve unshared information pooling in group decision making. The current research revises this view by hypothesizing that expertise assignment is beneficial when group members have cooperative goals, but is detrimental when group members have competitive goals. Three-person groups were confronted with a hidden-profile task. Members were either assigned experts or not and were instructed to either cooperate or compete with other members. The results confirmed that expertise decreased unshared information pooling and repetitions in competition, while the reverse was found in cooperation. This interaction effect was mediated by self–other difference in perceived competence. Thus, expertise favours or hinders information sharing in group decision making as a function of members’ cooperative or competitive goals.