In animal models of hepatocellular carcinoma (HCC), deficiency of S-adenosylmethionine (SAMe) increased the risk of HCC whereas administration of SAMe reduced HCC. The aim of this trial was to determine whether oral SAMe administration to patients with hepatitis C cirrhosis would decrease serum α-fetoprotein (AFP) level, a biomarker of HCC risk in hepatitis C. This was a prospective, randomized, placebo-controlled, double-blind trial of SAMe, up to 2.4 g/d, for 24 weeks as compared with placebo among subjects with hepatitis C cirrhosis and a mildly elevated serum AFP. Primary outcome was change in AFP between baseline and week 24. Secondary outcomes included changes in routine tests of liver function and injury, other biomarkers of HCC risk, SAMe metabolites, markers of oxidative stress, and quality of life. One hundred ten subjects were randomized and 87 (44 SAMe and 43 placebo) completed treatment. There was no difference in the change in AFP during 24 weeks among subjects receiving SAMe as compared with placebo. Changes in markers of liver function, liver injury, and hepatitis C viral level were not significantly different between groups. Similarly, SAMe did not change markers of oxidative stress or serum glutathione level. SAMe blood level increased significantly among subjects receiving SAMe. Changes in quality of life did not differ between groups. Overall, this trial did not find that SAMe treatment improved serum AFP in subjects with advanced hepatitis C cirrhosis and a mildly elevated AFP. SAMe did not improve tests of liver function or injury or markers of oxidative stress or antioxidant potential.