Progressive degrees of metabolic alterations are frequent in cirrhosis impairing peripheral tissue and body composition. Hepatocellular carcinoma worsens protein wasting and malnutrition. A normal energy production rate and an abnormal substrate oxidation rate are well-known findings in cirrhosis; however, no data are available on cirrhotic patients with hepatocellular carcinoma. The aim of this study was to measure oxidative metabolism in cirrhotic patients with and without hepatocellular carcinoma and to investigate the correlation between energy production rate, respiratory quotient and nutritional state. Thirteen male cirrhotic patients with hepatocellular carcinoma (8 well-nourished and 6 malnourished) were compared with 17 cirrhotic patients without hepatocellular carcinoma ( 11 well-nourished and 6 malnourished) and six controls who were age and sex matched. A diagnosis of malnutrition was made if the fat mass percentage was reduced to less than 20% of the patient's body weight. Indirect calorimetry was performed between 8 and 10 AM, after a 12-hr fast, for 30 min (with a 10-min steady-state period), and measured energy production rate was calculated according to Weir's formula. Body composition was assessed by means of the Durnin and Womersley formula. Anthropometry and bioelectric impedance analysis showed no variations in kilograms of fat-free mass in our malnourished patients. Our data show that, when the energy production rate is measured while the patient is at rest and corrected for fat-free mass, the energy requirements of cirrhotic patients and cirrhotic patients with hepatocellular carcinoma matched that of the controls, regardless of nutritional state. A significant reduction (p < 0.01) of respiratory quotient was documented in the presence of malnutrition both in cirrhotic patients and cirrhotic patients with hepatocellular carcinoma. Well-nourished cirrhotic patients and well-nourished cirrhotic patients with hepatocellular carcinoma had normal oxidative patterns. (HEPA-