Anemia is a frequent complication of cancer and its associated treatment. Although its occurrence is well documented in the chemotherapy setting, the prevalence and nature of anemia in the radiation oncology setting have been inadequately characterized. Preliminary findings from an ongoing retrospective study at Beth Israel Medical Center in New York indicate that mild-to-moderate anemia (ie, hemoglobin levels of 10 to 12 g/dL) is common at presentation for radiation therapy and increases in prevalence and severity during the course of radiation treatment. The symptoms of mild-to-moderate anemia, particularly fatigue, can substantially impair the quality of life of cancer patients. Furthermore, an extensive body of literature has documented an association between low hemoglobin levels and poor locoregional tumor control and survival following curative-intent radiation therapy. Greater efforts by radiation oncologists to document and treat anemia in patients undergoing radiation therapy may provide an opportunity to improve postradiation outcomes and well-being.