Fatigue is a common, often debilitating, side effect of cancer chemotherapy. Pharmacologic vitamin C has been used as an alternative treatment for the disease itself but its effects on fatigue have not often been documented. Here we report on the case of a woman with recurrent breast cancer, undergoing weekly chemotherapy, with lethargy as a major symptom. Vitamin C (50 g/session) was administered twice weekly and quality of life and multidimensional fatigue symptomology questionnaires were undertaken. Dramatic decreases in fatigue and insomnia were observed, as well as increased cognitive functioning. There were no adverse side effects of i.v. vitamin C.