Recent case reports of individuals with early-onset damage to the prefrontal cortex have suggested that such early insults could result in severely impaired social behaviour in later childhood and adolescence. The investigators speculated that the acquisition of complex social conventions and moral rules had been impaired. In a large cohort of children, we sought to determine whether early focal brain insults might result in clinically significant behavioural or emotional problems. This study reports on 39 children with pre- or perinatal-onset unilateral brain damage (focal lesion) from cerebral infarction or intraparenchymal haemorrhage, using the Achenbach Child Behavior Checklist to assess the presence or absence of behavioural and emotional difficulties. Two-thirds of the subjects had left hemisphere (LH) lesions and one-third had right hemisphere (RH) lesions. Age range was 4.0-15.4 years at the time of questionnaire completion. Their results were compared with those of 54 control children. Analyses were conducted on focal lesion versus controls, RH versus LH lesion, frontal versus non-frontal lesion, and seizure versus non-seizure groups. When the effect of IQ was partialled out, there were no significant differences on the nine Behavior Problem scales, the Internalizing-Externalizing dichotomy or the Total Problem score for any of the group comparisons. Our subjects showed no evidence of clinically significant behavioural or emotional problems, even when the frontal lobe was involved. Individuals with more extensive and bilateral damage may be at higher risk of significant behavioural and emotional dysfunction than were those in our study population. In future studies of brain-behaviour relationships in developing children, all potential causes for any observed behavioural abnormalities, such as genetic and environmental factors and toxin exposure, must be considered before concluding that specific anatomical lesions are causally related to specific behavioural outcomes.