Anemia is a hematologic abnormality commonly discussed during the treatment of childhood cancer, but its incidence has not been previously reported. As the basis for determining the incidence of anemia, this retrospective review of medical records combined databases containing the records of all patients 1 to 18 years of age with newly diagnosed neuroblastoma, rhabdomyosarcoma, Hodgkin disease, Ewing sarcoma, or osteosarcoma from two pediatric oncology centers. Data from 405 patients were included in the analysis of hemoglobin at the time of diagnosis. Across diagnoses, 51% to 74% of patients were anemic using the Centers for Disease Control and Prevention age- and sex-specific values to define anemia. The long-term complications of anemia in children with cancer are unknown. Further investigation of the clinical significance of anemia, including its impact on quality of life, is warranted.