Oral and systemic infections arising from the oral cavity are significant problems in clinical management of patients undergoing leukemia treatment. However, there is significant disparity in the reported incidences of development of periodontal infections. Evidence is limited to those showing the systemic influence of periodontal infection in neutropenic patients. This study indicated an association between febrile neutropenia (FN) and periodontitis in a case in which periodontal treatment in the intervals between chemotherapy cycles reduced FN in subsequent courses of chemotherapy and hematopoietic transplantation (HCT). Periodontal treatment was performed in a 61-year-old man with advanced periodontitis, who received HCT following three cycles of chemotherapy. After recovery from neutropenia induced by initial chemotherapy, periodontal treatment was performed in each chemotherapy interval period. Following extraction of teeth with severe advanced periodontitis, all teeth were subjected to periodontal pocket curettage and root planning, which are common periodontal treatments to reduce periodontal pockets harboring anaerobic periodontal bacteria, before HCT. Periodontal treatment successfully reduced periodontal pockets from 4.1 +/- 1.5 mm to 3.0 +/- 0.6 mm, which was almost within the healthy range (< 3.0 mm), before HCT. The frequency of FN decreased significantly with increasing cycles of chemotherapy, and decreases in FN corresponded to progress of periodontal treatment. Blood cultures obtained a total of 12 times throughout leukemia treatment were all negative. The observations reported here indicate the importance of periodontal treatment in clinical management of patients undergoing leukemia treatment to prevent FN, although all blood cultures were negative.