Objective: To explore corpus callosum (CC) developmental differences by ultrasound in late-onset small fetuses compared with adequate for gestational age (AGA) controls. Study Design: Ninety four small (estimated fetal weight <10th centile) and 71 AGA fetuses were included. Small fetuses were further subdivided into fetal growth restriction (IUGR, n = 64) and small for gestational age (SGA, n = 30) based on poor perinatal outcome factors, that is, birth weight <3rd centile and/or abnormal cerebroplacental ratio and/or uterine artery Doppler. The entire cohort was scanned to assess CC by transvaginal neurosonography obtaining axial, coronal and midsagittal images. CC length, thickness, total area and the areas after a subdivision in 7 portions were evaluated by semiautomatic software. Furthermore, the weekly average growth of the CC in each study group was calculated and compared. Results: Small fetuses showed significantly shorter (small fetuses: 0.49 vs. AGA: 0.52; p < 0.01) and smaller CC (1.83 vs. 2.03; p < 0.01) with smaller splenium (0.47 vs. 0.55; p < 0.01) compared to controls. The CC growth rate was also reduced when compared to controls. Changes were more prominent in small fetuses with abnormal cerebroplacental Doppler suggesting fetal growth restriction. Conclusions: Neurosonographic assessment of CC showed significantly altered callosal development, suggesting in-utero brain reorganization in small fetuses. This data support the potential value of CC assessment by US to monitor brain development in fetuses at risk.