Liver steatosis is a common finding in patients infected with hepatitis C virus (HCV). Host and viral factors have been associated with steatosis, but their relative contributions have not been clearly addressed. It has been suggested that steatosis plays a role in the progression of liver fibrosis. Aims - To assess: a) factors associated with steatosis in patients infected with hepatitis C virus; b) their impact on liver fibrosis. Patients and methods - Three hundred and fourteen untreated patients were included. Lifetime alcohol consumption was estimated. Liver fibrosis, inflammation and necrosis were assessed using the METAVIR score. Body mass index (BMI) was determined. The scoring system for steatosis was as follows: 0, no steatosis; 1, less than 10%; 2, 10% to 30%; 3, 30% to 70%; 4, more than 70% of hepatocytes affected. Results - In univariate analysis, steatosis was associated with elevated BMI (P = 0.001), excessive alcohol intake (P = 0.005), genotype 3 (P < 0.001) and moderate to severe histological activity (P = 0.01). Multivariate analysis showed that steatosis correlated with two independent factors: genotype 3a (OR = 60.7; 95% Cl: 7.6-483.4) (P < 0.001) and BMI (OR = 4.86; 95% Cl: 1.8-13.15) (P = 0.002). In univariate analysis, severe fibrosis (F2-F3-F4) was associated with older age (p < 10(-5)), male gender (P = 0.001), disease duration (P < 0.006), BMI (P < 10(-4)), alcohol intake (p < 10(-6)), severity of histological activity (p < 10(-5)) and steatosis (p < 10(-6)). In multivariate analysis, three independent factors were associated with severe fibrosis: disease duration > 10 years (OR = 3.17; 95% Cl: 0.65-15.4) (P = 0.015), presence of steatosis (OR = 3.17; 95% Cl: 1-9.99) (P < 0.049) and genotype 3a (OR = 5.56; 95% Cl: 1.4-22.1) (P = 0.015). Conclusion - In patients with chronic hepatitis C, steatosis is significantly associated with genotype 3 infection and high BMI Steatosis is an independent risk factor associated with severe fibrosis These results have major implications for the management of patients with chronic hepatitis C.