Infections identified between 1981 and 1983 in a hospital's medical/surgical, pediatric, neonatal, coronary care, and cardiac surgery ICUs were compared. Among 14,360 admissions, 1840 infections occurred in 1360 patients. Total infection rates ranged from 1.0% (cardiac surgery ICU) to 23.5% (medical/surgical ICU). Rates of ICU-acquired infection ranged from 0.8% (cardiac surgery ICU) to 11.2% (medical/surgical ICU), indicating that only about half of infections in the latter unit were acquired from within. Primary bacteremias comprised 14.5% of neonatal ICU infections, a rate 500% higher than in other ICUs. Meningitis and genitourinary infections were more common in pediatric and coronary care ICUs. Candida and Pseudomonas species and Klebsiella-Enterobacter-Serratia were most common in the medical/surgical ICU. Survival rate of infected patients was over 87% in pediatric and neonatal ICUs, compared with only 55.4% in the medical/surgical ICU. These differences in types and rates of infection have an important bearing on infection-control activities in the ICU, and also provide a yardstick against which similar institutions can gauge their ICU infection status.