Many countries in Europe have created national systems for the surveillance of healthcare associated infections (HCAI). The Hospitals in Europe Link for Infection Control through Surveillance (HELICS) has provided a standardised approach to surveillance of HCAI and formed a 'network of networks' to enable data from hospitals contributing to national networks also to be submitted to the HELICS database. This paper describes the set of surgical site infection surveillance data collected in 2004. It includes 111,361 operations in six categories of surgical procedure from 14 countries. The analysis demonstrates that incidence density provides a better measure for comparison than cumulative incidence as it takes some account of difference in length of post-operative stay and post-discharge surveillance. Comparisons should also take account of differences in mix of procedures, variation in risk factors and sensitivity of case finding. This rich dataset provides a unique opportunity to explore variation in rates of SSI and improve understanding of factors that impact on inter-country comparisons.