There have been various reports on the association of hepatitis C virus (HCV) infection with B lymphocyte proliferative disorders, such as non-Hodgkin lymphoma (NHL). We experienced a case (Case 1) of anti-HCV antibody (HCV-Ab)-positive NHL in which HCV nonstructural protein 3 (NS3) expression was observed in lymphoma tissue at the time of recurrence and in which the serum HCV RNA level exhibited a transient increase prior to recurrence. We investigated the HCV RNA genome in lymphoma tissue in Case 1, and it could be detected at recurrence. We also investigated HCV NS3 protein expression in lymphoma tissue and changes in serum HCV RNA level during the clinical course in four other cases of HCV-Ab-positive NHL treated in our hospital. We examined lymphoma tissues for HCV NS3 protein expression in four of the five cases, but it was not identified except for in Case 1 at recurrence. In three cases with no recurrence, serum HCV RNA levels showed a tendency to decrease after completion of chemotherapy and became stable thereafter. Further studies are necessary to clarify the association between serum HCV RNA and the onset and exacerbation of NHL.