Hepatitis C virus is known to be a risk factor for the development of B-cell non-Hodgkin lymphoma. Studies investigating the prevalence of hepatitis C virus in lymphoma report controversial results, depending on the geographical area. Monoclonal B lymphocytosis is an asymptomatic condition which can evolve into malignant lymphoma, characterized by the presence of a circulating clonal B population. It can be detected by flow cytometry and it is found at higher prevalence in hepatitis C virus-infected patients than in the general population. In the literature, there are only a few studies investigating its prevalence in hepatitis C infected patients and in Romania, such a study hasn’t been carried out before. We conducted a prospective study on 50 hepatitis C virus-infected patients from the Regional Institute of Gastroenterology and Hepatology Prof. Dr. Octavian Fodor. Clinical and laboratory data were collected from the medical files. Flow cytometric analysis was carried out at the Immunology Department of the Emergency County Hospital Cluj Napoca. We have found a prevalence of 22% of monoclonal B lymphocytosis. There were no statistical differences between patients with or without monoclonality, except for the lower leucocyte count (p=0.04) and the more increased liver echogenicity in patients with monoclonality (p=0.02). All of the 3 subtypes of monoclonal B lymphocytosis were found. Increased prevalence of monoclonal B lymphocytosis in patients with hepatitis C virus infection sustains the virus role in lymphomagenesis, but further studies are needed to analyze the rate of transformation into lymphoma in these patients.