BACKGROUND: We evaluated the comparative efficacy and safety of venlafaxine extended release (ER) and fluoxetine in the acute and continuation phases of treatment. METHODS: In this multicenter, double-blind study, outpatients with recurrent unipolar major depression were randomly assigned to receive venlafaxine ER (75-300 mg/day; n = 821) or fluoxetine (20-60 mg/day; n = 275). After a 10-week acute treatment phase, responders entered a 6-month continuation phase of ongoing therapy with double-blind venlafaxine ER (n = 530) or fluoxetine (n = 185). In the acute phase, the primary outcome was response, defined as a 17-item Hamilton Depression Rating Scale (HDRS) score < or =12 or > or =50% decrease from baseline; the secondary outcome was remission, defined as a HDRS score < or =7. In the continuation phase, the primary outcome was the proportion of patients who sustained response or remission. Secondary measures included time to onset of sustained response or remission (i.e., meeting criteria at two or more consecutive visits), relapse rates, and quality-of-life measures. RESULTS: At the acute treatment phase end point, response rates were 79% for both venlafaxine ER and fluoxetine; remission rates were 49% and 50% for venlafaxine ER and fluoxetine, respectively. In the continuation phase, response rates were 90% and 92%, and remission rates were 72% and 69% for venlafaxine ER and fluoxetine, respectively. Rates of sustained remission at the end of the continuation phase were 52% and 58% for venlafaxine ER and fluoxetine, respectively. CONCLUSION: Venlafaxine ER and fluoxetine were comparably effective during both acute and continuation phase therapy.