background. Accurate data on costs attributable to hospital-acquired infections are needed to determine their economic impact and the cost-benefit of potential preventive strategies. objective. To determine the attributable costs of surgical site infection (SSI) and endometritis (EMM) after cesarean section by means of 2 different methods. Design. Retrospective cohort. setting. Barnes-Jewish Hospital, a 1,250-bed academic tertiary care hospital. patients. There were 1,605 women who underwent low transverse cesarean section from July 1999 through June 2001. Methods. Attributable costs of SSI and EMM were determined by generalized least squares (GLS) and propensity score matched-pairs by means of administrative claims data to define underlying comorbidities and procedures. For the matched-pairs analyses, uninfected control patients were matched to patients with SSI or with EMM on the basis of their propensity to develop infection, and the median difference in costs was calculated. Results. The attributable total hospital cost of SSI calculated by GLS was $3,529 and by propensity score matched-pairs was $2,852. The attributable total hospital cost of EMM calculated by GLS was $3,956 and by propensity score matched-pairs was $3,842. The majority of excess costs were associated with room and board and pharmacy costs. Conclusions. The costs of SSI and EMM were lower than SSI costs reported after more extensive operations. The attributable costs of EMM calculated by the 2 methods were very similar, whereas the costs of SSI calculated by propensity score matched-pairs were lower than the costs calculated by GLS. The difference in costs determined by the 2 methods needs to be considered by investigators who are performing cost analyses of hospital-acquired infections.