The effectiveness of group psychotherapy was measured by comparing ihe institutional behavior of 46 experirnental subjects and 46 controls. The experimental group consisted of inmates at a maximum security, adult institution who were randomly chosen from the subject pool, and who were then offered the opportunity to participate in group therapy. As a result, experimental subjects showed significantly better institutional adjustment. In addilion, subjects' motivation and need for therapy were measured. Need for therapy correlated significantly with institutional adjustment, and motivation for therapy correlated with therapy attendance in the experimental group. However, subjects who had low motivation and need for therapy showed just as much gain from therapy as did subjects with high motivation and need.