An analysis of risk factors for nosocomial infections (NI) was carried out using data from the first national prevalence survey on NI in Germany. Fourteen thousand, nine hundred and sixty-six patients, with a total of 543 NI, were included. Urinary tract infections (UTI), lower respiratory tract infections (LRTI), surgical site infections (SSI) and primary septicaemia (PS) were analysed. UTI were significantly associated with unconsciousness, age, prior operation, hospital size and female sex (P < 0.1). LRTI were significantly associated with chronic airway disease, intensive care units, unconsciousness, polytrauma, prior operation, cardiovascular disease, malignancy and absence of infection on admission. The department, age, diabetes mellitus, male sex and hospital size were risk factors for SSI. The department, prior operation and unconsciousness were significantly associated with PS. An investigator effect was observed for LRTI and PS. Although no final conclusions from a risk factor analysis based on prevalence data can be drawn the results support stratification of NI for routine surveillance.