Nosocomial infection rates were computed for 5,031 patients at an oncology center during a 20-month period. Twelve percent of the patients developed nosocomial infections, accounting for a total of 802 infections. The overall incidence of nosocomial infections during this study period was 6.27 infections per 1,000 patient days. The highest incidence of nosocomial infections was found in patients having acute myelogenous leukemia (30.49 infections per 1,000 patient days); bone and joint cancer (27.27 infections per 1,000 patient days); and liver cancer (26.58 infections per 1,000 patient days). The respiratory tract was the most common site of infection, followed by blood-stream, surgical wound, and urinary tract infections. Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, and coagulase-negative staphylococci were most frequently implicated as pathogens. The distribution of specific types of infection according to underlying malignancy was also tabulated. These data provide nosocomial infection rates, common pathogens, and sites of infection for cancer patients, thus assisting in directing appropriate therapy for these patients.