To investigate the association of the diffusion-weighted MR imaging characteristics of fetal preCG and gestational age. Forty-four fetuses with normal brain MRI findings were included in the study. Gestational ages ranged from 18 to 36 weeks (mean 25.2 weeks). All exams were performed with a 1.5-T scanner using a body array coil during free maternal breathing without sedation. Precentral gyrus was defined as the hyperintense strip anterior to the central sulcus, on the superior section of axial brain images at the level of superior frontal cortex. The presence of preCG hyperintensity was noted as observed/subtle/not observed at different b values (500, 1000 s/mm(2)) and on apparent diffusion coefficient (ADC) maps and compared to the imaging characteristics of the superior frontal cortex. Precentral gyrus was first detected at 25 weeks as a hyperintense strip on DWI and hypointense strip on ADC maps. Display of preCG b 1000 s/mm(2) images were better than b 500 s/mm(2). Between 25 and 27 weeks, in 40% of fetuses preCG was observed on one hemisphere, and it was evident bilaterally in 60% of cases. Starting from the 28th week, preCG was observed on both hemispheres in 100% of cases. Diffusion weighted imaging helps better understanding of the evolution of fetal preCG. The hyperintense preCG strip starts to appear at 25 weeks, and when interpreting fetal DWI after 28 weeks this may be a sign to be sought for in all fetuses and an indicator for normal development. (C) 2012 The Japanese Society of Child Neurology. Published by Elsevier B.V. All rights reserved.