['Fatigue is an important determinant of altered quality of life in patients affected by chronic hepatitis C or the irritable bowel syndrome (IBS).', 'In this study, we aimed at determining the contributory role of plasma levels of leptin and carnitine on fatigue in chronic hepatitis C and IBS.', 'We enrolled 81 patients with chronic hepatitis C, 42 with IBS and 44 healthy subjects. Fatigue was evaluated using the Fatigue Impact Scale questionnaire. Body composition was assessed through impedance analysis. Plasma carnitine and leptin were measured.', 'Fatigue scores were significantly more elevated in patients with chronic hepatitis C and IBS than in healthy subjects. Patients with chronic hepatitis C but not IBS, had significant lower plasma levels of total and free carnitine adjusted for fat mass compared with healthy subjects. In patients with chronic hepatitis C and not with IBS, fatigue scores were negatively correlated with plasma levels of carnitine. Levels of free carnitine were significantly and independently associated with the severity of fatigue in patients with chronic hepatitis C [OR=2.019, P=0.02, CI 95% (1.01-1.23)].'] Is plasma carnitine associated with fatigue in chronic hepatitis C but not in the irritable bowel syndrome?