Abstract The surveillance of surgical wound infection (SWI) may be undertaken for a number of purposes which include evaluating changes in practice, studying the epidemiology of SWI and for assessing the quality of health care. Purchasers require this information from providers as an indicator of the quality of care. Surveillance of SWI can also have a role in audit, by setting standards and comparing observed practice with agreed standards. The level of SWI can be the standard, and the collection, analysis and interpretation of data (undertaken during surveillance) could be the means for measuring the standard. In a surveillance programme, data collection is often the most time consuming and difficult element and requires considerable planning. Initially, the data to be collected should be defined. This will be influenced by the purposes of surveillance, the ways the events (SWI) are defined, the data required to produce meaningful analyses and criteria used for identifying the patient. After the data has been defined, data collection methods should be chosen. The importance of assessing the accuracy and limitations of data collection methods in local settings is stressed. Only then is it possible to be sure that the data is a reliable basis on which to base decisions which promote the quality of health care.