We performed a randomized controlled trial to evaluate the safety and efficacy of enoxaparin, a low-molecular-weight heparin, in preventing portal vein thrombosis (PVT) in patients with advanced cirrhosis. In a nonblinded, single-center study, 70 outpatients with cirrhosis (Child-Pugh classes B7-C10) with demonstrated patent portal veins and without hepatocellular carcinoma were assigned randomly to groups that were given enoxaparin (4000 IU/day, subcutaneously for 48 weeks; n = 34) or no treatment (controls, n = 36). Ultrasonography (every 3 months) and computed tomography (every 6 months) were performed to check the portal vein axis. The primary outcome was prevention of PVT. Radiologists and hepatologists that assessed outcomes were blinded to group assignments. Analysis was by intention to treat. At 48 weeks, none of the patients in the enoxaparin group had developed PVT, compared with 6 of 36 (16.6%) controls (P = .025). At 96 weeks, no patient developed PVT in the enoxaparin group, compared with 10 of 36 (27.7%) controls (P = .001). At the end of the follow-up period, 8.8% of patients in the enoxaparin group and 27.7% of controls developed PVT (P = .048). The actuarial probability of PVT was lower in the enoxaparin group (P = .006). Liver decompensation was less frequent among patients given enoxaparin (11.7%) than controls (59.4%) (P < .0001); overall values were 38.2% vs 83.0%, respectively (P < .0001). The actuarial probability of liver decompensation was lower in the enoxaparin group (P < .0001). Eight patients in the enoxaparin group and 13 controls died. The actuarial probability of survival was higher in the enoxaparin group (P = .020). No relevant side effects or hemorrhagic events were reported. In a small randomized controlled trial, a 12-month course of enoxaparin was safe and effective in preventing PVT in patients with cirrhosis and a Child-Pugh score of 7-10. Enoxaparin appeared to delay the occurrence of hepatic decompensation and to improve survival. Copyright © 2012 AGA Institute. Published by Elsevier Inc. All rights reserved.