In recent years, it has been reported that acupuncture is useful for alleviating the symptoms of patients with hematological malignancies, but the safety of acupuncture for such patients has not been established. This study evaluated the risk of bleeding from acupuncture in patients with hematological malignancies accompanying thrombocytopenia. The authors performed a retrospective investigation of the medical records of patients with hematological malignancies who received acupuncture during hospitalization at the hematology department of a single medical center in Japan. The bleeding risk at the acupuncture site was evaluated in the following four groups according to the platelet count measured on the day of acupuncture treatment: (1) <20 × 10/μL, (2) 20-49 × 10/μL, (3) 50-99 × 10/μL, and (4) 100 × 10/μL or more. Occurrence of grade 2 or higher bleeding according to the Common Terminology Criteria for Adverse Events, version 5.0, within 24 h from the acupuncture session or before the next session was defined as an event, and the risk of occurrence of bleeding was examined in each group. Of 2423 acupuncture sessions conducted on 51 patients with hematological malignancies, 815 were included in the analysis. Ninety sessions were performed in the <20 × 10/μL platelet count group, 161 in the 20-49 × 10/μL group, 133 in the 50-99 × 10/μL group, and 431 in the 100 × 10/μL or more group. No bleeding event according to the authors' definition occurred in any of these groups. This study is the largest to date to assess the bleeding risk of acupuncture in patients with hematological malignancies accompanying thrombocytopenia. The authors considered that acupuncture could be safely performed without causing serious bleeding for patients with hematological malignancies accompanying thrombocytopenia.