Intrahepatic lymphocytic aggregates are observed in chronic hepatitis C as well as in autoimmune chronic hepatitis. Autoantibodies and autoimmune manifestations may occur in hepatitis C. It has been suggested that the lymphocytic aggregates play a role in the liver injury of chronic hepatitis C by an immune-mediated mechanism. We studied the occurrence of intrahepatic lymphocytic aggregates and of autoantibodies in a consecutive series of 128 patients with chronic hepatitis C. For the phenotypic characterization of the lymphocytic aggregates cryostat sections and microwaved paraffin embedded sections were immunostained with monoclonal antibodies directed against T cell subsets, B cells, killer/natural killer cells, follicular dendritic cells, and macrophages. Autoantibodies were tested by immunofluorescence (antinuclear, anti-smooth muscle, antimitochondrial) and by enzyme-linked immunosorbent assay (anti-soluble liver antigen, anti-liver/kidney microsome, anti-human receptor for asialoglycoprotein). Focal lymphocytic aggregates in portal tracts were observed in 76 of 128 (59%) patients. The cellular composition of the aggregates was constant: a core of B cells mixed with many T helper/inducer lymphocytes, and an outer ring was prominently formed by T suppressor/cytotoxic lymphocytes. A germinal center was rarely identifiable. The presence of lymphocytic aggregates was inversely correlated with the degree of fibrosis. Lymphocytic aggregates appeared more frequently in chronic persistent and chronic active hepatitis in comparison with cirrhosis and in the presence of bile duct damage. No correlation was found between lymphocytic aggregates and autoantibodies or other markers of autoimmunity. The lymphocytic aggregates are frequent in chronic hepatitis C. Their cellular composition is similar to that of primary lymphoid follicles in lymph nodes. Their presence does not seem to be correlated with features of autoimmunity. (Hepatology 1995; 22:389–394.)