An investigative analysis was carried out of the neuromotor and cognitive findings in a population-based study of low-birthweight infants (< 1750g) at 4 1/2 years of age to try to improve the understanding of the neuropathological basis of their deficits. Cluster analysis identified groups of children whose performance in the cognitive subscales of the British Ability Scales followed similar patterns, and also differentiated between children in neuromotor competence. Cluster membership correlated highly with language attainment, ability to copy shapes, behaviour as reported by parents and parents' and examiners' perception of attention span. Children in poorer-performing clusters were more likely to be born to mothers who had had a previous perinatal death, and were also more likely to have experienced septicaemia during the neonatal period. These findings are discussed in the light of evidence from the neuropathological and physiological literature.