['We have previously found that atorvastatin decreases liver injury markers in patients with nonalcoholic steatohepatitis. However, how atorvastatin treatment ameliorates the disease activity in nonalcoholic steatohepatitis patients remains unknown.', 'We examined here which anthropometric, metabolic and inflammatory variables were improved and related with amelioration of disease activity in atorvastatin-treated nonalcoholic steatohepatitis patients.', 'Forty-two biopsy-proven nonalcoholic steatohepatitis patients with dyslipidemia were enrolled. Patients were treated with atorvastatin (10mg/day) for 12 months.', 'Atorvastatin significantly decreased liver transaminase, γ-glutamyl transpeptidase, low-density lipoprotein-cholesterol, triglycerides, type IV collagen, and tumour necrosis factor-α levels, whilst it increased adiponectin and high-density lipoprotein-cholesterol. Atorvastatin improved nonalcoholic fatty liver disease activity score and increased liver to spleen density ratio. Multiple stepwise regression analysis revealed that γ-glutamyl transpeptidase, tumour necrosis factor-α and liver to spleen density ratio (inversely) were independently associated with nonalcoholic fatty liver disease activity score. Aspartate aminotransferase, low-density lipoprotein-cholesterol and nonalcoholic fatty liver disease activity score were independent determinants of decreased liver to spleen density ratio.'] Does atorvastatin improve disease activity of nonalcoholic steatohepatitis partly through its tumour necrosis factor-α-lowering property?