The relative role of perinatal factors (birthweight, gestational age, gender, asphyxia, mechanical ventilation and cerebral lesions), developmental factors (neuromotor development during the first 18 months of life) and environmental factors (socio-economic status and bilingualism) on cognitive abilities was evaluated in a cohort of preterm children who had been prospectively examined for haemorrhage (PVH) and periventricular leucomalacia (PVL) and followed-up to 5 years of age. Standardized neurological examinations and development assessment including tests of cognitive function were carried out. Major impairments could be ascribed to the presence of large PVL changes. Among the 226 children without major impairment, the overall incidence of neuropsychological anomalies (neuromotor, language, visual, auditory and behaviour anomalies) was 46.5% and did not differ within ultrasound groups (normal scans, PVH and small PVL). However, children with small changes of PVL presented more abnormal neuromotor development within the first 18 months of life and had more complex neuropsychological anomalies at 5 years. The multiple regression analysis (General Intellectual Index (GII) predicted = 113.7 - coefficient x social class - 8.5 x bilingualism - 5.5 x dystonia + 1.4 x gestational age + 8 x mechanical ventilation) showed that socioeconomic status was the most important factor affecting the General Intellectual Index (GII). The contribution of sex and cerebral lesions was not significant. As children grew-up, environmental factors seemed to overcome perinatal factors.