OBJECTIVE To evaluate the efficacy, safety and tolerability of sildenafil among Brazilian patients with hypertension treated with combinations of anti-hypertensive drugs. METHODS One hundred twenty hypertensive men aged 30 to 81 years old under treatment with 2 or more anti-hypertensive drugs and with erectile dysfunction (ED) lasting for at least 6 months were enrolled at 7 research centers in Brazil. Patients were randomized to receive treatment with either sildenafil or placebo taken 1 hour before sexual intercourse (initial dose of 50 mg, adjusted to 25 mg or 100 mg according to efficacy and toxicity). During the following 8 weeks, patients were evaluated regarding vital signs, adverse events, therapeutic efficacy, satisfaction with treatment and use of concurrent medications. RESULTS The primary evaluation of efficacy, which was based on responses to questions 3 and 4 of the International Index of Erectile Function, showed significant differences regarding treatment with sildenafil (p = 0.0002 and p < 0.0001, respectively). In the assessment of global efficacy, 87% of the patients treated with sildenafil reported improved erections, as compared with 37% of patients given placebos (p < 0.0001). The other secondary evaluations supported the results favoring sildenafil. The most frequent adverse events among patients treated with sildenafil were headaches (11.4%), vasodilation (11.4%) and dyspepsia (6.5%). There were no significant changes in blood pressure measurements in both groups. CONCLUSIONS Sildenafil is efficacious and safe for the treatment of hypertensive patients with ED who receive concurrent combinations of anti-hypertensive drugs.