Complications, prognosis, and efficacy of treatments were retrospectively studied in elderly patients, some of whom had lung, stomach, colon, pancreatic, and liver cancers. Hemoglobin concentration and characteristics of erythrocytes were measured for up to sixty months. Eighty-eight patients died of cancer, and malignant tumors were detected before death in 57. The average survival periods were 11 months for patients with gastric cancer. 9 months for those with colon cancer, and 7 months for those with lung cancer. Malignancies of the digestive organs and lung were often detected in elderly patients with anemia. In elderly people who were without cancer for more than 78 months the hemoglobin concentration did not change significantly, but in those with a malignancy the hemoglobin concentration continuously decreased. Patients with colon cancer who were given blood transfusions survived longer than those who were not given the transfusions, but the same was not true of patients with gastric or lung cancers. Iron therapy, however, was generally effective in patients with malignant tumors of the gastrointestinal tract. Among those who were near death, the red cell distribution widths differed significantly between patients with different types of carcinomas, but differences in mean corpuscular hemoglobin and in mean corpuscular volume were not statistically significant. In conclusion, hemoglobin concentration and characteristics of erythrocytes should not be neglected in the diagnosis and treatment of cancers in the elderly.