Objective. Survey of changes in the number of preterm and very low birth weight infants in the Netherlands in ten years. Design. Descriptive. Setting. TNO Preventie en Gezondheid, sector Jeugd, Leiden, the Netherlands. Method. All infants with a gestational age less than 32 weeks and (or) a birth weight less than 1500 g from the National Neonatal Register born in 1993 were selected, supplemented with data from a questionnaire for hospitals not taking part in the register. The data were compared with those on similar infants from the 'Project on preterm and small for gestational age' infants born in 1983. Results. The total number of preterm and very low birth weight infants increased from 1423 in 1983 to approximately 1882 in 1993. There was also an increase in terms of proportion, from 8.4 per thousand to 9.6 per thousand. The proportion of preterm infants never treated in a neonatal intensive care unit decreased from 40% in 1983 to 14% in 1993, probably due to increased centralization of neonatal intensive care facilities. In the same time mortality decreased for all gestational age categories. Conclusion. Both the total number and the survival of preterm and very low birth weight infants increased considerably over a decade. This caused a considerable increase in intensive care days and is therefore an important reason for the increased requirement of neonatal intensive care cots.