This review focuses on HCV infection in oncohematological patients. High risk of hepatitis C virus (HCV) infection within this group of patients was proved by a significantly (2.0–2.5 times) higher HCV infection rate in non-Hodgkin’s lymphoma patients compared to population data. Besides, the review demonstrates the importance of HCV in the development and progression of B-cell non-Hodgkin’s lymphomas, which is confirmed by its tumorigenicity. The paper reviews the variant of seronegative (occult) hepatitis С, which is characterized by HCV RNA detected in liver tissue and peripheral blood mononuclear cells by highly sensitive reverse transcription PCR with the absence of serum HCV and HCV RNA antibodies. In this case, patients can present a source of infection. Seronegative hepatitis С is detected in donor blood in 2.2–3.4 % of cases. This infection variant is identified in 20–85 % of oncohematological patients, which needs to be further examined. Comorbid HCV infection is a potential prognostic factor in oncohematological diseases. Oncohematological patients with comorbid chronic hepatitis C (CHC) show considerably worse survival as compared with patients without it. HCV infection is associated with increased complication rates in both chemotherapy and hematopoietic stem cell transplantation (HSCT). Immunochemotherapy, on the other hand, affects CHC exacerbation and progression. High efficacy and good tolerability of direct-acting antiviral agents (DAA) in CHC therapy opened new prospects for their wide use in cases of comorbid diseases. HCV treatment in patients after HSCT still remains an issue. The guidelines for CHC treatment are predominantly formulated with a view to antiviral pre-HSCT therapy which is not always feasible in real-world clinical practice. The review contains examples of effective use of DAA drugs before or after HSCT and a case of antiviral treatment administered simultaneously with HSCT.