This systematic review reports the results of three meta-analyses addressing the clinical efficacy of psychological interventions in breast cancer patients. Three outcome variables were examined: anxiety, depression and quality of life. Several moderator variables were found to both account for inter-trial heterogeneity and interact with treatment efficacy; methodological quality, prognosis, treatment type, orientation and duration. A clinically moderate treatment effect was found for anxiety (−0.40, 95% CI, −0.72 to −0.08, N = 1278). This was not robust to study quality, but remained stable for patients with more advanced disease. Short-term group therapy was more effective than longer term intervention and individual ones. A clinically moderate-to-strong effect was found in trials assessing depression (−1.01, 95% CI, −1.48 to −0.54, N = 1324). A more robust finding of −0.47 (95% −0.69 to −0.24) was based on methodologically more reliable studies treating patients with high psychological morbidity. Intervention was shown to have moderate effects on improving QOL (0.74, 95% CI, 0.12 to 1.37, N = 623), though it was not robust to study quality. Findings suggest that short-term treatments with a focus on coping may be more suitable for early breast cancer patients. Patients with advanced breast disease appear to benefit more from longer term interventions which emphasize support. Recommendations are also made for future clinical trials.