Volumetric analysis of brain images obtained from MRI was used to study cerebral development in 85 normal children and adolescents, 5 to 17 years of age, at the Kennedy Krieger Institute, Johns Hopkins University, Baltimore; and Thomas Jefferson School of Medicine, Philadelphia, USA. Boys’ brains were 10% larger than girls, and increased cortical grey matter contributed primarily to the larger brain volume. Age related changes included loss of cortical and subcortical grey volume and gain in white matter volume. Cerebral asymmetries were similar in both sexes: cortical and subcortical grey matter was prominent on the right side and CSF on the left. Total cerebral volume, particularly prefrontal grey matter, correlated with IQ. Subcortical grey matter volume showed a lesser but significant correlation with IQ variance. 
COMMENT. The finding that larger than normal brain volume is not always associated with superior cognitive function should allay fears that the investigators had any sexist bias in reporting boys’ brains to be 10% larger than girls. Examples cited include children with neurofibromatosis-1 and the fragile X syndrome, both characterized by macrocephaly and below average IQ.