This prospective study investigated the impact of group composition on the outcome of 2 forms of time-limited, short-term group therapy (interpretive, supportive) with 110 outpatients from 18 therapy groups, who presented with complicated grief. The composition variable was based on the patient's level of quality of object relations. The higher the percentage of patients in a therapy group who had a history of relatively mature relationships, the better the outcome for all patients in the group, regardless of the form of therapy or the individual patient's quality of object relations score. The findings have direct clinical implications for composing short-term therapy groups for outpatients with complicated grief and possibly for other types of group therapies and patient problems.