Of 55 consecutive long-term survivors of birth weight 500 to 999 g, complete psychologic and pediatric data were available for 54 children at 2 years corrected age and for 50 at age at least 5 1/2 years. At the latter age, 60% (30 of 50) were not impaired, 10% (five of 50) had severe sensorineural or intellectual impairments, 10% (five of 50) had mild to moderately impairment, and 20% (10 of 50) had minor neurobehavioural abnormalities. Sensorineural deafness in one child and bilateral blindness in one remained stable over time, but of six children with spastic cerebral palsy at 2 years, only three retained this diagnosis at 5 1/2 years. The mean Mental Developmental Index (MDI) on the Bayley Scales at 2 years was 91.1, significantly below the test mean; by 5 1/2 years the mean full scale of the Wechsler Preschool and Primary Scales of Intelligence (WPPSI) was 101.8. The MDI correlated highly with the full-scale WPPSI (r = 0.7), but for individual children it was not always an accurate predictor of 5-year ability. Between 2 and 5 1/2 years there was a substantial reordering within four categories of impairment: findings in 27 children were improved, four were judged to become more severely impaired over time, and 19 did not change. We conclude that our 2-year assessment often underrated the potential of the children as expressed at 5 1/2 years, and that 2 years is too early for reliable classification of children of birth weight 500 to 999 g.