The knowledge of the natural history of patients with hepatocellular carcinoma is important to estimate the prognosis at diagnosis and indicate the best therapy. Prognosis is related to tumour stage at diagnosis, degree of liver function impairment induced either by the tumour itself or by the underlying cirrhosis, general physical condition of the patients, and potential impact of therapy. Prognostic estimation should take into account all four aspects. Treatment is very relevant to be considered in patients with early stage tumours since surgical resection, transplantation or percutaneous ablation provide a high rate of complete responses and thus, improve survival. This might be as high as 50-75% at 5 years. Patients diagnosed at an intermediate/advanced stage will receive palliative treatment and prospective studies have recently redefined the outcome predictors of this stratum. Asymptomatic patients in whom the tumour has not invaded vessels or disseminated may reach a 50% survival at 3 years, while those with adverse predictors do not reach this time point. These data have to be taken into account not only in the conventional clinical practice, but also in the design and evaluation of prospective investigations that should be properly powered to reach an informative sample size. To achieve both aims, within the Barcelona Clinic Liver Cancer Group we have developed a staging system that combines prognosis prediction with decision making, thus becoming a useful tool both for practice and research.