BACKGROUND: A relationship between hepatocellular carcinoma (HCC) recurrence and serum alanine aminotransferase (ALT) in a group of hepatectomized patients has been reported. Another study suggested the development of HCC is more rapid in a high ALT group of hepatitis C virus (HCV)-associated cirrhotic patients. To find a relationship between ALT and HCC occurrence, we observed changes in ALT over a period of 6 years, in a group of non-cirrhotic, chronic hepatitis C (CHC) patients treated with anti-inflammatory drugs post interferon (IFN) therapy. METHOD: Eighty three CHC patients, with fibrosis stage 1, 2, 3 (F1, F2, F3) who had a partial (PR) or non-response (NR) to initial IFN therapy, were treated with anti-inflammatory drugs for 6 years. Over a period of 6 years HCC developed in nine patients. Of them, one belonged to F2 and eight to F3. Within the first 2 years HCC developed among two patients in F3. Multivariate analysis revealed that in F3, the 6 year average ALT activity (odds ratio 5.59; P<0.05) was the only significant variable associated with HCC occurrence. All other variables remained insignificant. Among the six F3 patients in whom HCC developed, the likelihood of HCC occurrence was found to be significantly higher (odds ratio 1.89; P<0.001) in patients who showed elevated ALT activity (>80 IU) two or more times during the 6 year period, compared to those with ALT (>80 IU) for less than 2 years. CONCLUSION: These findings suggest that continuous elevation of ALT seems to be important for HCC diagnosis. Patients with ALT >==80 IU for 2 years or more are at a greater risk of HCC development. It is necessary to continue treatment with anti-inflammatory drugs, following initial IFN therapy to suppress ALT below 80 IU, to prevent HCC occurrence or delay the time of HCC occurrence in order to prolong life.