Thirty-nine of 61 prospectively followed patients who had had acute non-A, non-B hepatitis in 1978 were clinically reexamined in 1991 and tested for antibodies to hepatitis C virus (anti-HCV) with a second generation ELISA and RIBA and for HCV RNA by PCR. Acute hepatitis C was diagnosed in stored sera from 1978 in 24 patients, who were found still to be anti-HCV positive in 1991, and 16 of them were also HCV RNA positive. The majority of anti-HCV positive patients with or without HCV RNA had elevated serum ALT levels 13 years after onset of their acute hepatitis C. After 13 years follow-up, 1.6% of the patients had died of end-stage liver disease, 8% of anti-HCV positive patients had histologically confirmed liver cirrhosis, 79% of anti-HCV positive patients were judged to have chronic infection, whereas 21% seemed to have recovered. To conclude, we found that a majority of our patients with acute symptomatic hepatitis C continued to be viraemic 13 years after onset of hepatitis C, and that all continued to be anti-HCV positive by second-generation ELISA.