Depression and erectile dysfunction (ED) often co-occur. Phosphodiesterase type 5 inhibitors are effective in men with ED and untreated depression, or ED secondary to antidepressants. This study evaluated sildenafil treatment in Canadian men with clinically diagnosed ED (Sexual Health Inventory for Men score ≤21) and mild-to-moderate untreated depressive symptoms [Beck Depression Inventory II (BDI-II) score 14–28], but excluding major depressive disorder. Pretreatment screening using the Sexual Health Inventory for Men and BDI-II showed that men with ED were more likely to have depression than men without ED, and ED severity was a predictor of depression (P=0.0226). Two hundred and two men were randomized to 6 weeks of double-blind treatment with placebo (n=98) or sildenafil (n=104), initial dose of 50 mg, adjustable to 25 or 100 mg. The men were evaluated on all domains of the International Index of Erectile Function and the Sex Effects Questionnaire, Global Efficacy Questions, and Event-log data. Compared with placebo, patients treated with sildenafil had significantly greater changes from baseline in BDI-II scores (P<0.001). All International Index of Erectile Function domains and the Sex Effects Questionnaire components were also significantly improved in sildenafil group (P<0.01). The most common adverse events included headache, dyspepsia, vasodilatation, and respiratory tract infections and were generally mild in intensity.