AimSSI is one of the most prevalent healthcare‐associated infections and is associated with extended hospital stays, increased need for reoperation and higher hospital readmission rates. Implementing systematic SSI surveillance can reduce these adverse outcomes. Implementing a surveillance system into a hospital is a complex intervention requiring that staff involved in a patient's perioperative journey have the knowledge of SSI prevention, the data required for surveillance, an understanding of how data informs quality improvement initiatives and their role in surveillance. The aim of this study was to evaluate the impact of a complex intervention on the knowledge and attitudes of healthcare professionals towards surgical site infection (SSI), SSI prevention and surveillance in a university hospital setting.DesignThe study used a quasi‐experimental pre‐test–post‐test design.MethodThe impact of a complex intervention was evaluated by measuring healthcare professionals' (n = 74) knowledge of and attitudes towards SSI and surveillance. Normalisation process theory (NPT) guided the study and the development of the intervention.ResultsThere was a statistically significant increase in scores on the knowledge of SSI and prevention from pre‐intervention to post‐test. The knowledge of risk factors scores at post‐test was significantly higher than that at pre‐intervention. Overall attitudes to SSI prevention and surveillance were good both pre‐intervention and post‐test but there was a significant change in the attitude of participants. The findings reveal an overall positive impact of the complex intervention on the knowledge and attitude of healthcare professionals relating to SSI, SSI prevention and surveillance; however, the extent of the change varied across items measured.