One hundred and thirteen long-term mentally ill clients receiving case management were investigated with regard to psychosocial and clinical predictors of changes in subjective quality of life during an 18-month follow-up. Better psychosocial functioning and fewer psychiatric symptoms at baseline predicted a greater improvement in quality of life. A larger decrease in symptom severity and a greater improvement in the social network during the follow-up were identified as the most important predictors of a greater improvement in subjective quality of life. The results of the study suggest that an emphasis should be put on effective symptom management, a reduction of needs for care and social support in order to fulfill the aims of improving subjective quality of life in patients receiving case management.