Diphenylhydantoin (DPH) therapy, often used in treating epileptic seizures, can cause anemia in some patients. A 26-year-old female suffered from convulsions due to encephalitis and was placed on DPH therapy. About two months after the initiation of DPH therapy, her hemoglobin level was 3.8 g/dL. Her anemia improved after the discontinuation of DPH, confirming that the anemia was caused by DPH. Pure red-cell aplasia (PRCA) combined with hemolytic anemia was indicated by results such as erythroid aplasia, an increased LDH level, and a decreased haptoglobin level. PRCA complicated by hemolytic anemia could be responsible for anemia associated with DPH.