Vilazodone is a selective serotonin reuptake inhibitor and 5-HT1A partial agonist approved for major depressive disorder (MDD) treatment in adults. This was a 10-week, multicenter, double-blind, placebo-controlled and active-controlled, fixed-dose trial (NCT01473381). Adult patients with MDD (Diagnostic and Statistical Manual of Mental Disorders, 4th ed., text revision criteria) were randomized 1 : 1 : 1 : 1 to vilazodone 20 or 40 mg/day, citalopram 40 mg/day, or placebo. Primary efficacy: Montgomery-Åsberg Depression Rating Scale (MADRS); secondary efficacy: Clinical Global Impressions-Severity and sustained response (MADRS total score≤12 for at least the last two consecutive double-blind visits). The intent-to-treat population comprised 1133 patients, (placebo=281; vilazodone 20 mg/day=288; vilazodone 40 mg/day=284; citalopram=280). MADRS and Clinical Global Impressions-Severity score change from baseline to week 10 was significantly greater for vilazodone 20 mg/day, vilazodone 40 mg/day, and citalopram versus placebo. Sustained response rates were numerically higher, but not significantly different, in all active treatment groups versus placebo. The most common adverse events (≥5% of vilazodone patients, twice the rate of placebo) were diarrhea, nausea, vomiting (vilazodone 40 mg/day only), and insomnia. Improved sexual function (Changes in Sexual Functioning Questionnaire scores) was seen in all groups; between-group differences were not significant. Vilazodone 20 and 40 mg/day demonstrated efficacy and tolerability in the treatment of MDD.