The aim of this study was to estimate the economic costs of healthcare-acquired surgical site infection (HA-SSI) and show how they are distributed between the in-hospital and post-discharge phases of care and recovery. A quantitative model of the epidemiology and economic consequences of HA-SSI was used, with data collected from a prospective cohort of surgical patients and other relevant sources. A logical model structure was specified and data applied to model parameters. A hypothetical cohort of 10 000 surgical patients was evaluated. We found that 111 cases of infection would be diagnosed in hospital and 784 cases would first appear after discharge. Of the total costs incurred, either 31% or 67% occurred during the hospital phase, depending on whether production losses incurred after discharge were included. Most of the costs incurred by the hospital sector arose from lost bed-days and only a small proportion arose from variable costs. We discuss the issues relating to the size of these costs and provide data on where they are incurred. These results can be used to inform subsequent cost-effectiveness analyses that evaluate the efficiency of programmes to reduce the risks of HA-SSI.