This report describes the results of a prospective study of nosocomial infection in 7,714 patients hospitalized during a 24-month period at a cancer treatment center. An overall nosocomial infection rate of 9.3% was observed with site-specific infection rates of 2.6% for urinary tract, 1.9% for surgical wound, 2.2% for bacteremia and 1.9% for respiratory tract infection. Within specific patient groups, the overall nosocomial infection rates observed were: 8.2% in medical patients, 14.9% in surgical patients and 1.5% in pediatric patients. Despite the markedly elevated nosocomial infection rate in surgical patients (P < 0.001), surgical wound infection rates were not unlike those observed in general hospitals: clean—2.4%, clean contaminated—5.8%, contaminated—13.2%, and dirty—11.8%. These observations provide evidence that institutions which provide medical care predominantly for cancer patients can expect to observe higher nosocomial infection rates than general care hospitals.