Background: In this double-blind randomized study, the analgesic effects of morphine alone and with methylprednisolone were examined in 72 patients undergoing arthroscopic knee surgery. Methods: At the end of arthroscopy, patients were allocated randomly to one of four groups to receive intra-articular administrations of saline, morphine 1 mg, morphine 5 mg or morphine 1 mg with methylprednisolone 40 mg. Preoperative and postoperative pain levels at rest and during movement (active flexion of the knee) were measured by a visual analogue scale (VAS). Postoperative analgesic requirements to alleviate pain were evaluated. Results: Pain scores were significantly lower for the patients who received 5 mg morphine and 1 mg morphine with 40 mg methylprednisolone than for those who received saline or 1 mg morphine. This was accompanied by a decrease in the postoperative consumption of analgesics and prolongation of the duration of pain relief. Conclusions: This study confirms that the analgesic effect of morphine given intra-articularly is dose dependent and that combination of methylprednisolone with morphine has an additive effect on analgesia.