Introduction: Hemorrhoidal disease occurs in 50% of people aged > 40 years and is the most common reason for anorectal surgery. Pain is the main complication. Multiple topical and systemic drugs have been investigated for pain control, but there is no ideal treatment. Metronidazole has been shown to decrease postoperative pain but is not used widely.Objective: To evaluate the effect of oral metronidazole versus placebo and to assess postoperative pain following hemorrhoidectomy.Material and methods: Controlled clinical trial in adult patients who underwent elective hemorrhoidectomy for grade III/IV hemorrhoids. Patients were assigned to receive metronidazole (500 mg q8 h orally; study group, SG) or placebo (control group, CG) for 7 days after surgery. Pain was assessed using a visual analog scale after surgery. Analgesic administration (time and use of analgesics) and resumption of daily life activities were also assessed.Results: Forty-four patients were included, 22 in each group. Postoperative pain differed significantly between the SG and CG at 6 h