BACKGROUND: Fatigue is one of the most common and distressing symptoms experienced by breast cancer survivors. Despite its prevalence, relatively little is known about the characteristics, etiology, or treatment of fatigue in breast cancer survivors. METHODS: This report reviews studies that assessed fatigue in breast cancer patients previously treated with adjuvant radiotherapy, adjuvant chemotherapy, or autologous bone marrow transplantation. RESULTS: A review of the literature suggests that breast cancer patients who undergo adjuvant chemotherapy or autologous bone marrow transplantation experience clinically significant levels of fatigue for months or even years following the completion of active treatment. In contrast, there is little evidence that patients who receive only regional therapy (ie, surgery plus adjuvant radiotherapy) experience clinically significant fatigue as a long-term treatment side effect. CONCLUSIONS: A growing body of evidence indicates that persistent fatigue can be a long-term side effect of certain forms of breast cancer treatment. The challenges for the future will be to determine the etiology of fatigue among breast cancer survivors and to develop interventions that are effective in preventing or reducing fatigue following breast cancer treatment.