ELBW (birth weight below 1000 g) neonates and have been well characterized and documented in the postnatal period, survivors (n = 140) will be matched with two controls. One control will be matched to sex, birth year and residential area and will be suggested by the index patient, the second control will be age and sex matched from the area of the field center. All children considered are currently between 8 and 15 years of age.