In a long-term prospective study, 39 preterm children born before 35 completed weeks of gestation and 23 full-term children were followed up at 4, 9 and 19 years of age. Psychometric evaluation of the cognitive development at 4 years of age showed that the preterms fell within the normal range, although their performance was inferior to that of the full-terms. This difference between the groups was not found at 9 and 19 years of age. Within the preterm group there was no correlation between the test results and birthweight, gestational age, prenatal or perinatal optimality scores. Full-terms had better scholastic performance at the end of compulsory schooling, while there was no difference at 19 years of age. At 19 years of age, about 1/3 of the children in both groups rated themselves as having had attention deficits during their childhood and adolescence. In this group of moderately immature, low-risk children, preterm birth without major physical or mental disabilities poses a developmental risk that seems to have the greatest impact during the preschool years and then gradually attenuates.