BACKGROUND In this clinical trial, polyethylene glycol (PEG) solution was compared with lactulose in the treatment of hepatic encephalopathy in patients with cirrhosis. METHODS This randomized controlled trial was performed on 40 patients in two groups. The patients in the lactulose group received either 20-30 grams of lactulose orally or by a nasogastric tube, or 200 grams of lactulose enema by a rectal tube. The patients in the PEG–lactulose group received the same amount of oral or rectal lactulose, plus 280 grams of PEG in 4 liters of water orally as a single dose in 30-120 minutes. Serial physical examinations, hepatic encephalopathy scoring algorithm (HESA), blood level of ammonia, and serum biochemical studies were used to evaluate the severity of hepatic encephalopathy. RESULTS In comparison with lactulose alone, PEG-lactulose could improve HESA score in 24 hours more effectively (p =0.04). Overall, PEG-lactulose regimen was associated with a decrease in length of hospital stay compared with lactulose treatment (p =0.03) but in subgroup analysis we found that PEG-lactulose regimen could only decrease the length of hospital stay in women significantly (p =0.01). CONCLUSION The use of PEG along with lactulose in comparison with lactulose alone is more effective in the treatment of hepatic encephalopathy in patients with cirrhosis and results in more rapid discharge from hospital.