To assess the importance of nosocomial infections as a contributory cause of death in patients who die in the hospital, we studied the hospital course of 100 consecutive patients who died at Columbia-Presbyterian Medical Center and 100 consecutive patients who died at Hackensack Hospital. The epidemiologic patterns of infection were similar although the institutions provide care for different types of patients. There were 88 nosocomial infections in 63 patients. When the nosocomial infection was causally related or contributed to death, infection of the lower respiratory tract was predominant in 31 of 52 (60 per cent) instances. When the nosocomial infection was unrelated to death, urinary tract infection was predominant in 13 of 36 (36 per cent) infections. Among those who died with nosocomial infection, 42 of 63 (67 per cent) patients were terminal on admission and were typically in their 60's with metastatic carcinoma. The 21 patients who were not terminal on admission were typically in their late 70's and had complications of arteriosclerotic cardiovascular disease. Pneumonia was the most frequent nosocomial infection related to death. There is need to devise a pneumonia prevention program that identifies those at high risk and reduces the chance of aspiration of pharyngeal secretions and spread of virulent bacteria from person to person.