Epigenetic alterations are a common hallmark of human cancer. Single epigenetic markers are starting to be incorporated into clinical practice; however, the translational use of these biomarkers has not been validated at the 'omics' level. This is strikingly the case in hepatocellular carcinoma (HCC) which represent the most common primary malignant tumor of the liver. Alpha-fetoprotein (AFP) has been widely used as a diagnostic marker of HCC; however, according to international guidelines (AASLD, EASL), AFP is unsufficiently sensitive or unsufficiently specific for use in a screening assay. Aberrantly methylated DNA sequences frequently occur in tumors and are detected in the circulation of cancer patients by polymerase chain reaction (PCR). SEPT9 is a significant epi-driver gene in liver carcinogenesis. The SEPT9 gene is a key regulator of cell division and tumor suppressor whose hypermethylation is associated with carcinogenesis. SEPT9 is involved in the onset of rat hepatocarcinogenesis and SEPT9-promoter hypermethylation was reported in HCC in man. SEPT9 expression is turned on in cells throughout the body and absent or diminished by aberrant promoter methylation in several types of cancer. Through an initial proof-of-concept pilot study from France and an independent replication study from Germany, we showed that the circulating cell-free DNA methylation-based epigenetic biomarker mSEPT9 is a promising plasma biomarker for diagnosing HCC in cirrhotic patients. The aim of the SEPT9-CROSS study is to confirm the diagnostic accuracy of the biomarker in a large-scale study of 630 cirrhotic patients recruited in the participating centers.