Background: Surgical Safety Checklists (SSC) have been implemented widely across 132 countries since 2008. Yet, despite associated reductions in postoperative complications and death rates, implementation of checklists in surgery remains a challenge. The aim of this study was to assess the impact of a patient safety programme over time on SSC use and incidence of clinical errors. Design: A prospective longitudinal design over three time points and a retrospective secondary analysis of clinical incident data was undertaken. Methods: We implemented a patient safety programme over 4 weeks to improve surgical teams' use of the SSC. We undertook structured observations to assess surgical teams' checklist use before and after programme implementation and conducted a retrospective audit of clinical incident data 12 months before and 12 months following implementation of the programme. Results: There were significant improvements in the observed use of the SSC across all phases, particularly in sign-out where completion rates ranged from 79.3% to 94.5% (p<0.0001) following programme implementation. Across clinical incident audit periods, 33 019 surgical procedures were performed. Based on a subsample of 64 cases, clinical incidents occurred in 22/16 264 (0.13%) before implementation and 42/16 755 (0.25%) cases after implementation. The most predominant incident after programme implementation was inadequate tissue specimen labelling (23/42, 54.8%). Clinical incidents resulted in minimal or no harm to the patient. Conclusions: The benefit in using a surgical checklist lies in the potential to enhance team communications and the promotion of a team culture in which safety is the priority.