Nonselective β-blockers are very effective in preventing first variceal bleeding in patients with cirrhosis. Treatment with isosorbide-5-mononitrate (IS-MN) plus propranolol achieves a greater reduction in portal pressure than propranolol alone. The present multicenter, prospective, double-blind, randomized, controlled trial evaluated whether combined drug therapy could be more effective than propranolol alone in preventing variceal bleeding. A total of 349 consecutive cirrhotic patients with gastroesophageal varices were randomized to receive propranolol + placebo (n = 174) or propranolol + IS-MN (n = 175). There were no significant differences in the 1- and 2-year actuarial probability of variceal bleeding between the 2 groups (propranolol + placebo, 8.3% and 10.6%; propranolol + IS-MN, 5% and 12.5%). The only independent predictor of variceal bleeding was a variceal size greater than 5 mm. However, among patients with varices greater than 5 mm (n = 196), there were no significant differences in the incidence of variceal bleeding between the 2 groups. Survival was also similar. Adverse effects were significantly more frequent in the propranolol + IS-MN group due to a greater incidence of headache. There were no significant differences in the incidence of new-onset or worsening ascites or in impairment of renal function. In conclusion, propranolol effectively prevents variceal bleeding. Adding IS-MN does not further decrease the low residual risk of bleeding in patients receiving propranolol. However, the long-term use of this combination drug therapy is safe and may be an alternative in clinical conditions associated with a greater risk of bleeding.