Purpose: Prolonged and disabling fatigue is prevalent after cancer treatment, but the early natural history of cancer-related fatigue (CRF) has not been systematically examined to document consistent presence of symptoms. Hence, relationships to cancer, surgery, and adjuvant therapy are unclear. Patients and Methods: A prospective cohort study of women receiving adjuvant treatment for early-stage breast cancer was conducted. Women (n = 218) were enrolled after surgery and observed at end treatment and at 1, 3, 6, 9, and 12 months as well as 5 years. Structured interviews and self-report questionnaires were used to record physical and psychologic health as well as disability and health care utilization. Patients with CRF persisting for 6 months were assessed to exclude alternative medical and psychiatric causes of fatigue. Predictors of persistent fatigue, mood disturbance, and health care utilization were sought by logistic regression. Results: The case rate for CRF was 24% (n = 51) postsurgery and 31% (n = 69) at end of treatment; it became persistent in 11% (n = 24) at 6 months and 6% (n = 12) at 12 months. At each time point, approximately one third of the patients had comorbid mood disturbance. Persistent CRF was predicted by tumor size but not demographic, psychologic, surgical, or hematologic parameters. CRF was associated with significant disability and health care utilization. Conclusion: CRF is common but generally runs a self-limiting course. Much of the previously reported high rates of persistent CRF may be attributable to factors unrelated to the cancer or its treatment. �� 2012 by American Society of Clinical Oncology.