The purpose of the study was to evaluate brain myelination by measuring the magnetization transfer ratio (MTR) and to measure grey (GMV) and white matter volume (WMV) in macrocephalic children with neurofibromatosis type 1 (NF1). Seven NF1 patients (aged 0.65-16.67 years) and seven age- and gender-matched controls were studied. A three-dimensional (3D) gradient echo sequence with and without magnetization transfer (MT) prepulse was used for MTR assessment. Volume measurements of GM and WM were performed by applying segmentation techniques on T2-weighted turbo spin echo images (T2WI). MTR of unidentified bright objects (UBOs) on T2WI in cerebellar white matter (52.8+/-3.3), cerebral peduncles (48.5+/-1.5), hippocampus (52.6+/-1.1), internal capsule (55.7+/-0.3), globus pallidus (52.7+/-3.9), and periventricular white matter (52.6+/-1.2) was lower than in the corresponding areas of controls (64.6+/-2.5, 60.8+/-1.3, 56.4+/-0.9, 64.7+/-1.9, 59.2+/-2.3, 63.6+/-1.7, respectively; p<0.05). MTR of normal-appearing brain tissue in patients was not significantly different than in controls. Surface area (mm(2)) of the corpus callosum (809.1+/-62.8), GMV (cm(3)) (850.7+/-42.9), and white matter volume (WMV) (cm(3)) (785.1+/-85.2) were greater in patients than in controls (652.5+/-52.6 mm(2), 611.2+/-92.1 cm(3), 622.5+/-108.7 cm(3), respectively; p<0.05). To conclude, macrocephaly in NF1 patients is related to increased GMV and WMV and corpus callosum enlargement. MTR of UBOs is lower than that of normal brain tissue.