The aim of this work is to analyze costs of surgical site infections (SSI) in selected orthopedic procedures. Cases of SSI after hip and knee prosthesis detected in the year 2005 in the specialistic hospital situated in the southern Poland was taking into account in this study. CDC's definitions for detection of SSIs cases were used in this study. There were 22 cases of SSIs detected in the whole year. Estimated direct costs of additional hospitalization reached 131,000 PLN. Costs of antibiotics used for treatment SSI cases were equal to 38 249 PLN. Hospital acquired infections are extremely costly side effect of hospitalization so their detailed and continuous surveillance is necessary. But it won't be possible without systemic change of management and organization of health care sector in Poland.