Anemia in cancer patients has been under-recognized and little studied in Japan. To gain some insight into cancer-related anemia in Japanese patients undergoing outpatient chemotherapy, we performed a single-center retrospective study of the prevalence and incidence of anemia in 148 patients with solid tumors treated at the Kyoto University Hospital Outpatient Oncology Unit. We classified the cases of anemia in accordance with the National Cancer Institute Common Terminology Criteria for Adverse Events (version 3.0). Of 148 patients, 65 (44%) were anemic at the start of chemotherapy, 19 (13%) of whom had anemia of grade 2 or higher. Chemotherapy further increased the number of anemic patients, with 125 (84%) being anemic at some point during chemotherapy, and 61 (41%) of these having anemia of grade 2 or higher. Among the 83 patients without anemia at the start of chemotherapy, 60 (72%) developed anemia during chemotherapy, 15 (18%) of whom had anemia of grade 2 or higher. This is the first report showing a high prevalence and incidence of anemia in Japanese patients undergoing outpatient chemotherapy. Better recognition and management of cancer-related anemia are required in Japan. To this end, randomized controlled trials evaluating the effects of erythropoietic agents on patients' survival and quality of life are necessary.