The suitability of tramadol suppositories for inclusion in our hospital formulary for the treatment of mild to moderate post-operative pain was evaluated. In an open randomized trial, rectal tramadol was compared with our standard treatment acetaminophen/codeine suppositories. We expected tramadol to be equally effective as our current standard but with fewer side effects. Forty patients were treated with either tramadol suppositories 100 mg 6 hourly (qds) or acetaminophen/codeine suppositories 1000/20 mg qds.Patients were comparable with regard to demographic data and type of surgery and anaesthesia. Post-operative pain was scored with the aid of a Visual Analogue Scale before each drug administration, at rest and during movement. Side effects, notably nausea and vomiting, were recorded by interviewing the patients and by inspecting the nursing report. There was no difference in pain scores between the two groups. The incidence of nausea and vomiting was significantly higher in the tramadol-treated (84%) than in the acetaminophen/codeine treated group (31%). The relative risk of experiencing an episode of nausea under treatment with tramadol was 2.7 (95% confidence interval: 1.3–5.3; P=0.0001) as compared with acetaminophen/codeine. We conclude that for acute treatment of mild to moderate post-operative pain frequent nausea and vomiting makes tramadol suppositories less suitable than acetaminophen/codeine.