The effects of early unilateral brain lesions on subsequent intellectual functioning were explored in hemiplegic children with congenital or acquired lesions. For congenital hemiplegics who sustained damage pre- or perinatally, lower intellectual functioning (IQ) was most highly associated with longer elapsed time since lesion. Moreover, including lesion size as an additional predictor of IQ did not account for significantly more variance than elapsed time since lesion alone. In contrast, for acquired hemiplegics who sustained damage after birth, lower intellectual functioning was highly associated with larger lesion size. In this group neither elapsed time since lesion nor age at testing accounted for significantly more IQ variance than lesion size alone. Possible effects of maturational factors and functional plasticity are considered in interpreting this pattern of results.