 The primary outcome measure will be 6-month survival. The secondary outcome measures will be the proportion of transplanted patients, the occurrence of complications bacterial infection, renal failure, hepatic encephalopathy and gastrointestinal bleeding. All adult patients with severe cirrhosis might be randomized after written consent. Pregnant persons; patient who has been treated with a quinolone in the month before the inclusion, allergy to quinolones, hepatocellular carcinoma, or HIV infection will not be included. Patients receive either norfloxacin or placebo once a day for 6 months. Three hundred and ninety-two patients are necessary to decrease 6-month mortality rate from 40 in the placebo group to 25 in the norfloxacin group with a beta risk of 90 and an alpha risk of 5. Patients will be followed-up every month during 6 months and at 9 and 12 months. 