Sixteen risk factors for nosocomial pneumonia were prospectively studied in 582 intubated patients in a surgical intensive care unit (ICU) to identify patients at particularly high risk. Overall, pneumonias developed in 94 of the patients (16%). Significant risk factors for pneumonia were mechanical ventilation for more than 72 h, impaired consciousness or co-operation, specific therapeutic interventions as a marker of severe underlying diseases (dopamine/dobutamine greater than or equal to 5 micrograms/kg.min, barbiturate therapy for treatment of elevated intracranial pressure, continuous i.v. antiarrhythmic or antihypertensive drugs), and pre-existing pulmonary abnormalities (P less than 0.001). The acquisition of postoperative pneumonia was further associated with male sex, ASA class IV and a history of smoking, but statistical significance was lost after stepwise logistic regression. Longer operative procedures, thoracic or upper abdominal surgery, longer preoperative hospital stay, low serum albumin concentration on admission, prior antibiotics, old age, obesity, low weight, malignant disease, and steroid treatment did not influence the incidence of pneumonia. In this study we were able to identify a subpopulation of intensive care patients at particularly high risk for pneumonia.