We detected a 24.6 per cent nosocomial infection rate (222 infections in 138 infants) among 904 infants hospitalized for over 48 hours in a regional newborn intensive-care during 41 months of surveillance. Surface infections accounted for 40.1 per cent of the total, pneumonia for 29.3 per cent, bacteremia for 14.0 per cent, surgical-wound infection for 8.1 per cent, urinary-tract infection for 4.5 per cent, and meningitis for 4.0 per cent. Staphylococcus aureus (47.3 per cent) and gram-negative enteric bacilli (45.1 per cent) were the most common organisms recovered. Nosocomial infection rates were significantly higher in infants with a birth weight less than 1500 g (P less than 0.001). The mortality rate in infants with any nosocomial infection was 33 per cent in contrast to 14 per cent in non-infected babies (P less than 0.001). Nosocomial infections are a major problem in newborn intensive-care units.