Case-control study for evaluation of cost and outcome of nosocomial surgical site infection in primary hip arthroplasty during a period of 5 years. Mean hospitalization time in the orthopedic service was 54 days for cases, and 13 days for control (p<0.05). Mean hospitalization time in Intensive Care Unit (ICU) was 1.1 days for cases. There were 0.83 post primary surgery interventions in cases, and a mean of 2.08 bacteriological cultures in each case. Controls didn't have hospitalizations in the ICU surgical reinterventions nor cultures necessary. The mean cost of infected patients was US $: 6,174.8. Mean cost in controls was US $: 2,354.7. The excess of cost due to infections was US $: 2,354.7 on the average. Outcomes in cases were: normal function 30.8%; moderate or serious sequelae 46.2%; death rate 15, 4%. The measured parameters contributed to raise case costs, and they caused an unsatisfactory outcome for two third of the patients.