Objectives: To test the long-term efficacy and safety of venlafaxine extended-release (ER) in preventing recurrence in patients with major depression. Method: This multiple-phase study, entitled "Prevention of Recurrent Episodes of Depression With Venlafaxine for Two Years" (PREVENT), was conducted from December 2000 through July 2005 in patients with recurrent unipolar depression (DSM-IV) who were initially randomly assigned to double-blind treatment with venlafaxine ER (75 mg/day to 300 mg/day) or fluoxetine (20 mg/day to 60 mg/day) for 10 weeks of acute treatment. Responders then received 6 months of continuation treatment. Those who remained responders were then enrolled into a 12-month maintenance period. Venlafaxine ER responders were randomly assigned to receive double-blind treatment with venlafaxine ER or placebo. Fluoxetine responders were not randomly assigned but continued taking fluoxetine in order to maintain the blind during the maintenance study. Time to recurrence of depression (17-item Hamilton Rating Scale for Depression total score > 12 and < 50% reduction from acute phase baseline) with venlafaxine ER versus that of placebo were compared. Results: The efficacy evaluable sample consisted of 129 patients in each group. The mean daily dose of venlafaxine ER was 224.7 mg (SD = 66.7). The cumulative probability of recurrence through 12 months, based on the primary definition, was 23.1% (95% CI = 15.3 to 30.9) for venlafaxine ER and 42.0% (95% CI = 31.8 to 52.2) for placebo (p = .005, log-rank test). Conclusion: Patients who had been successfully treated with venlafaxine ER during acute and continuation therapy were significantly less likely to experience recurrence with venlafaxine ER than with placebo over a 12-month maintenance treatment period. Clinical Trials Registration: ClinicalTrials.gov identifier NCT00046020.