The purpose of this study was to determine the effectiveness of a couple-based intervention on the quality of life (QOL) of early-stage breast cancer patients and their partners. A randomized controlled design was used to assign couples to either the hospital standard social work services (SSWS) or a couple-based intervention, the Partners in Coping Program (PICP). QOL was measured at three times during the first year after the diagnosis. A series of analyses of covariance revealed that QOL of patients and partners in the PICP arm improved at time 2 and time 3 and was consistently higher than the QOL of couples in the SSWS arm, controlling for QOL at time 1. However, differences between the two arms on QOL were not statistically significant. Patients in the PICP who were in relationships of shorter lengths and were receiving chemotherapy made the greatest gains in their QOL, suggesting that these types of patients would benefit more from a couple-based approach to their illness. On the basis of the findings, the authors suggest future directions for intervention research and for social work practitioners who are looking for efficient and effective ways to deliver psychosocial services to cancer patients.