Influenza virus infections (IVIs) are an important cause of complications and death in immunocompromised patients, but the incidence and risk factors for IVIs in hematological diseases including benign diseases are not fully understood. We retrospectively investigated IVIs in patients with hematological diseases who visited our hematology outpatient department between 2012 and 2019. In 4,864 outpatients, 81(1.67%) IVIs were identified. The incidence of IVIs was 4.82 (95% confidence interval [CI], 3.85-5.96) per 1,000 person-years, with significantly higher rates in post-allogeneic transplant patients (21.0, 95% CI, 12.8-32.5). Progression to lower respiratory tract infection (LRTI) was observed in 7 (8.6%) of 81 patients with IVIs. In a univariate logistic regression analysis, LTRI was associated with age ≥60 years and moderate to severe chronic GVHD. Patients after hematopoietic stem cell transplantation may be at a higher risk for IVIs. Advanced age exacerbated the effects of IVIs on hematological diseases.