To investigate the influence of human immunodeficiency virus (HIV) coinfection on preexisting long-term chronic C hepatitis (HCV) 68 liver biopsies from 22 HIV/HCV-coinfected, 13 HIV- and 33 HCV-monoinfected patients and 71 livers obtained at autopsy from 26 HIV/HCV-coinfected and 45 HIV-monoinfected patients were studied by histo- and immunohistochemistry. All HIV patients had reached the advanced stage of immunodeficiency (stage III CDC), except for 3 haemophilias (stage II CDC). HCV infection was associated with a higher degree of portal, periportal and lobular inflammation-regardless of whether there was concurrent HIV infection. HIV/HCV coinfection was associated with a significantly higher rate of granulocytic cholangiolitis than HCV and HIV monoinfection (P < 0.05), a histological feature uncommon in C hepatitis. In HIV/HCV coinfection cholestasis was a predominant histological feature. HCV monoinfection and HCV/HIV coinfection were associated with the highest fibrosis index. In HIV/HCV coinfection centrilobular fibrosis was significantly more marked than in HCV monoinfection (P < 0.05), suggesting an HIV-associated fibrogenic effect. Patients with chronic C hepatitis showed a significantly increased rate of posthepatitic cirrhosis compared with the patients without HCV infection (P < 0.05). At autopsy, 10 of the 20 HIV/HCV-coinfected haemophiliacs had developed cirrhosis because of chronic C hepatitis, whereas cirrhosis was found in only 2 of 6 HIV/HCV-coinfected non-haemophiliacs (1 case of chronic B and C hepatitis, and 1 case of chronic alcohol abuse). No cirrhosis was observed in the 45 autopsy patients with HIV monoinfection. The findings suggest that HIV coinfection aggravates the course of preceding long-term chronic C hepatitis by a more marked (centrilobular) fibrosis. HIV/HCV-coinfected patients are threatened by a higher rate of posthepatitic cirrhosis-particularly in multitransfused haemophiliacs-and cholestatic hepatopathy.