During the years 1978-89, all surviving extremely low birthweight infants (BW less than 1000 g, ELBWI) in the region of Southern Finland were admitted to the Children's Hospital, University of Helsinki and followed up to six years. The number of liveborn ELBWI increased from 30 to 50/year during the first and last third of the follow-up. During the same twelve year period, the number of the surviving infants increased from 8 to 25/year, with the number and proportion of infants with birthweights of less than 800 g and with gestational ages of less than 27 weeks increasing from 3 to 15/year. Despite of the greater proportion of smaller infants the proportion of infants without intraventricular hemorrhage increased from 50 to 85%. The proportion of children with normal neurodevelopment at two years increased from 40-70% during the first five years of the study, to 63-84% during the last three years of the study. The proportion of children with major disabilities decreased from 28 to 8%. The factors associated with poor neurodevelopment were sepsis, year of birth, intraventricular hemorrhage, and birthweight. The neurological status at one year was a valid predictor of the outcome: at four years 94% of the infants were assessed and normal remained normal as neurologically abnormal remained abnormal or slightly abnormal. The neurologically normal ELBWI were tested at six years: visuomotor coordination was immature in 50%, emotional immaturity was found in 25% and delay of language development in 13%. In our unit increased survival of ELBWI infants has not been associated with an increase in the number of ELBWI infants with handicaps.(ABSTRACT TRUNCATED AT 250 WORDS)