Anemia is common in patients with cancer. This systematic literature review of reports published in 1966 through February 2003 identified the prevalence of anemia in specific cancers and assessed the impact of anemia on survival and quality of life (QOL). Studies about chemotherapy-induced anemia were excluded. Anemia prevalence varied widely; most studies found that between 30% and 90% of patients with cancer had anemia. Prevalence was affected strongly by the definition of anemia: 7% of patients with Hodgkin disease had anemia when the condition was defined as a hemoglobin level <90.0 g/L; as many as 86% of patients had anemia when it was defined as a hemoglobin value <110.0 g/L. Prevalence varied by cancer type and disease stage: 40% of patients with early-stage colon tumors and nearly 80% of patients with advanced disease had anemia. Patients with anemia had poorer survival and local tumor control than did their nonanemic counterparts in 15 of 18 studies. In 8 of 12 studies, patients without anemia (most treated with epoetin) needed fewer transfusions. QOL was positively correlated with hemoglobin levels in 15 of 16 studies. There was no significant difference in treatment toxicity between patients with and without anemia. Tumor hypoxia, which has been associated with resistance to radiation therapy and chemotherapy, may stimulate angiogenesis, leading to poor local control of tumors and increased morbidity and mortality. Treatment of anemia may have a significant impact on patient survival and QOL. However, a standard definition of anemia is needed, as is research about the effect of anemia on cancer progression.