The majority of deaths in normally formed infants occur in extremely low birth weight infants (< 1000 g). Survival rates for these infants have improved greatly but still vary from centre to centre and accurate local outcome figures are important for counselling parents and upholding standards of care. In the Rotunda Hospital, Dublin, over the 6 year period from 1 January 1990 to 31 December 1995, there were 34 474 deliveries over 500 g birthweight. One hundred and twenty-six of these were normally formed infants between 500 g and 999 g. Our objective was to analyse the factors influencing survival in these extremely low birthweight (ELBW) infants. Overall survival in the group was 63%. The most significant factors influencing survival to 28 days were gestation and birthweight. Survival increased from 33% at 24 weeks to 100% at 28 weeks' gestation and from 29% at 500-599 g to 87% at 900-999 g birthweight. Having controlled for gestational age, none of the following variables had a significant effect on survival: year of birth; gender; multiple pregnancy; 1-minute Apgar score; maternal age; parity; use of antenatal steroids; a history of antepartum haemorrhage, pre-eclamptic toxaemia or prolonged rupture of membranes. A 5-min Apgar score > 5 increased the chance of survival by 3.97 (95% CI: 1.46- 10). Both mode of delivery and incidence of chorioamnionitis had an influence on survival which varied according to the gestational age. A larger cohort of survivors would illustrate the effect of these variables more clearly.