Metabolic syndrome (MS) is a newly identified risk factor in chronic liver disease (CLD) and hepatocellular carcinoma (HCC). The aim of this study was to analyze the pathological characteristics of HCC and nontumoral liver in patients with MS as the only risk factor for liver disease in comparison with those that developed in the course of other CLDs in order to provide further insight into the physiopathology of HCC associated with MS. HCC patients with features of MS as the only risk factor for liver diseases (MS group, n = 31) were compared to HCC patients with overt causes of CLD (CLD group, n = 81) or without causes of CLD (cryptogenic group, n = 16) who underwent surgical resection during the same period of time. Among the patients of the MS group, there were 30 males and 1 female. In comparison with the patients with HCC of the CLD group, the patients with MS were older (mean age: 67± 7 versus 59 ± 14 years, P < 0.01), and the background liver was significantly more often free of significant fibrosis (F0–F2: 65% in the MS group versus 26% in the CLD group, P < 0.001). In addition, HCCs associated with MS were more often well differentiated (65% versus 28%, P < 0.001). Five HCCs, all from the MS group, developed on a preexisting liver cell adenoma, with three of them showing typical histological features of telangiectatic adenoma. Conclusion: This study shows that HCCs in patients with features of MS as the only risk factor for liver disease have distinct morphological characteristics and mainly occur in the absence of significant fibrosis in the background liver. In addition, some of them arise through malignant transformation of a preexisting liver cell adenoma. (HEPATOLOGY 2009.)