Hepatocellular carcinoma (HCC) is one of the most common cancers in the world. The majority of patients who develop HCC have underlying cirrhosis, which suggests that cirrhosis itself represents a preneoplastic condition. Nevertheless, whereas patients with cirrhosis of any origin are at increased risk of developing HCC, those with chronic hepatitis B or C infection seem to be at greatest risk. Patients with cirrhosis resulting from chronic alcohol use, hemochromatosis, autoimmune hepatitis, or alpha-1 antitrypsin deficiency have less risk of developing this cancer, and some hepatic diseases, such as primary biliary cirrhosis and Wilson's disease, do not predispose affected persons to an appreciable risk of developing HCC. Certain histological features, such as liver cell dysplasia and macroregenerative nodules, may represent preneoplastic alterations of hepatocytes, but these changes do not seem to be a necessary step in the evolution of liver cancer. The pathogenesis of HCC is unclear, but seems to involve several steps. Hepatitis B virus infection may result in the malignant transformation of hepatocytes by some directly oncogenic mechanism, whereas other necroinflammatory conditions probably predispose to the development of HCC through the introduction of genetic alterations coupled with a reduction of genetic repair functions. Screening patients at risk for the development of HCC using alpha fetoprotein measurements and ultrasonography is widely practiced despite inconclusive evidence of efficacy. If screening is performed, the program used should be tailored to the perceived risk for a particular patient.