Background/Aims: Hepatitis C is an escalating global health problem. The recommended treatment regimen is associated with considerable expense, adverse effects and poor efficacy in some patients. Complementary therapies are widely promoted for and used by patients with hepatitis C. The aim is to systematically assess the efficacy of complementary therapies in treating chronic hepatitis C. Methods: Systematic searches were conducted in six databases, reference lists of all papers were checked for further relevant publications and information was requested from experts. No language restrictions were imposed. Results: Twenty-seven eligible randomised clinical trials were located involving herbal products and supplements. No randomised clinical trials were identified for any other complementary therapy. In 14 of the trials, patients received interferon-alpha in combination with the complementary therapy. Less than half the trials (11/27) were of good methodological quality. Compared with the control group, significant improvements in virological and/or biochemical response were seen in trials of vitamin E, thymic extract, zinc, traditional Chinese medicine, Glycyrrhiza glabra and oxymatrine. Conclusions: We identified several promising complementary therapies, although extrapolation of the results is difficult due to methodological limitations. More research is warranted to establish the role of these and other therapies in the treatment of hepatitis C. (C) 2003 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.