Assessing fetal cerebral biometry is one means of ascertaining that the development of the fetal central nervous system is normal. Norms have been established on large cohorts of fetuses by sonographic and neurofetopathological studies. Biometric standards have been established in MR in much smaller cohorts. The purpose of this paper is to analyse methods of measuring a few parameters in MR [biparietal diameter (BPD), fronto-occipital diameter (FOD), length of the corpus callosum (LCC), atrial diameter, transverse cerebellar diameter, height, anteroposterior diameter and surface of the vermis] and to compare US and MR in the assessment of fetal cerebral biometry.