The aim of this study was to examine the cognitive outcome of children with congenital and acquired early-onset unilateral brain lesions associated with hemiparesis. The neuropsychologic evaluation was done using the NEPSY test battery on 37 children with hemiparesis and 13 sex- and age-matched healthy controls. Compared to the controls, children with left-sided brain lesions had significant delay in phonologic and language functions, while children with right-sided brain lesions performed more poorly in visual and spatial skills and in somatosensory functions. There were more left-handed children in the former (6 of 23) than in the latter (1 of 14) group. There was no significant difference in cognitive outcome between children with congenital and acquired lesions. The cognitive outcome of boys and that of children with active epilepsy was more affected. Overall, the patients showed impairment in many cortical functions and diffuse cognitive delay compared to controls and the side of lesion, active epilepsy, and male gender were significant factors in predicting cognitive outcome.