In a double-blind, randomized, controlled study, 61 patients who received a standardized anaesthetic for day case arthroscopic knee surgery were studied. Group T (n=31) received tramadol 1.5 mg kg−1, and group F (n=30) received fentanyl 1.5 μg kg−1 at the induction of anaesthesia. All patients also received 20 mL of intra-articular bupivacaine 0.5% at the end of surgery. Assessments were made of pain at rest and on movement, analgesic requirements and side-effects at hourly intervals up to 6 h and by means of a postal questionnaire at 24 h and 48 h post-operatively. Group F had higher pain scores than group T at 4 h only [VAS 3.3 (1.6–5.5) vs. 2.4 (1–4), P=0.039, respectively; median (interquartile range)]. There were no other significant differences between the groups in terms of pain scores, supplemental analgesic requirements or incidence of side-effects. We conclude that tramadol offers little benefit clinically compared with fentanyl when used at induction of anaesthesia for day case arthroscopic knee surgery. Further studies are indicated in patients with more severe pain to determine the role of tramadol in post-operative analgesia.