Implementation of the World Health Organisation checklists have reduced errors, however, the impact of pre-operative briefings on adverse events has not been assessed. A prospective case control study assessing the association between pre-operative briefings and minor, potentially major and major adverse events was performed in two phases. Phase one involved prospective data collection for trauma and orthopaedic lists over 2 weeks. Changes were implemented and following this, the study was repeated (phase two). 41 lists were audited during phase one and 47 lists in phase two. Adequate pre-operative briefings were performed in 10/41 lists (24%) in phase one. There was a significant association between the occurrences of intra-operative adverse events (n=37) when a briefing was not performed (p=<0.01), and when a briefing was performed incompletely (p=0.01). In phase two, after staff re-education and policy change, briefings were found to be adequate in 38/47 lists (81%) with the occurrence of only three minor adverse events. Team familiarity also improved significantly (p=0.02). Inadequate pre-operative briefings are associated with increased minor adverse events and are detrimental to team familiarity. On the basis of our findings we recommend that all surgical units perform pre-operative briefings.