A three-year cohort of extremely low-birthweight (ELBW, less than 1000g) survivors born between 1st January 1979 and 31st December 1981 were followed prospectively at one, two and five years of age, corrected for preterm birth. 57 of 110 infants survived, and 53 children were still alive at five years. The diagnoses of cerebral palsy, blindness, deafness and developmental delay fluctuated markedly according to age at developmental assessment. Although 13 of the 53 children were found to have impairments at five years, only seven were identified at one year, while 17 were identified at two years. In relation to the five-year assessment, impairments were underestimated at one year and developmental delay was overestimated at two years, which suggest that valid and reliable estimation of adverse neurodevelopmental sequelae among ELBW survivors may not be possible until school-age.