The inhibition of neural input by infiltration of local anaesthetic around the operation site prior to the trauma of an operation may reduce subsequent pain post-operatively. Prevention of the normal phenomenon of central and peripheral sensitisation in the nervous system stops the post operative hypersensitivity state that manifests as a decrease in the pain threshold at the site of injury. The underlying clinical principle is for therapeutic intervention to be made in advance of the pain rather than as a reaction to it Thirty six patients undergoing day case unilateral knee arthroscopy between October 2000 and March 2001 were studied. All patients gave written informed consent. They were randomised into 2 groups using block randomisation to ensure equal group sizes. The sealed envelope technique was used. The pre-operative group had 10ml 0.25% bupivicaine infiltrated around the arthroscopy portal site following induction of general anaesthesia (G.A.), the post-operative group received 10ml 0.25% bupivicaine after the procedure but before reversal of the G.A. The injection technique and G.A. used were standardised. Pain was assessed using a 10cm Visual Analogue Score (VAS) at pre-operative, 1, 2 and 24h post-operative. At each assessment the patients were blinded to the previous scores that they had submitted. Oral analgesic use in the post-operative 24 hours was also recorded. There were 18 patients in each group. Demographic details did not differ between the 2 groups. One patient in the post-operative group was excluded, as intravenous sedation was required in recovery due to an extreme anxiety state. The mean Visual Acuity Pain Scores (VAS) were lower in the post-operative group (1.3) compared to the pre-operative group (1.58) at pre-operative assessment. However this difference was not statistically significant (p =0.5607). At 1h post op the mean VAS in the post op group was 1.58 and in the pre op group 2.59 (p =0.18). The mean VAS at 2h post op in the pre op group was 1.76 compared to 1.82 in the post op group (p =0.9932). At 24h the pre op group had a lower mean VAS (2.25) than the post op group (2.4). This difference was however not statistically significant (p =0.7418). Analysis of the postoperative analgesia requirement in both groups failed to reveal a statistically significant difference (p =0.3965). In day case knee arthroscopy under general anaesthesia there is no beneficial role in the use of pre-emptive local anaesthetic infiltration around the arthroscopy portal sites as compared to post-operative infiltration.