An analysis was made of all cases of infection among 181 neonates admitted to the neonatal intensive care unit (NICU) during one year. Twenty-four per cent had an infection on admission; their infections correlated with prolonged ruptured membranes and the degree and site of colonization. The predominant organisms found in perinatal infections were Staphylococcus aureus, Group B streptococci and Escherichia coli. Thirty per cent acquired a hospital infection. This correlated with the length of the period of instrumentation. The majority of the hospital-acquired infections was caused by Gram-positive cocci (micrococci, Staph. saprophyticus, Staph. aureus, forming 65 per cent of the total), E. coli and Pseudomonas aeruginosa. Most hospital infections were nosocomial and not auto-infection. The outcome of the neonates with hospital infection was good, except for those with pseudomonas infection. Acquisition of hospital infection prolonged the period of hospitalization up to twice that required for neonates without infection.