We reported on thirteen children affected with malformative syndromes associated with mental retardation. MRI examination showed in all of them different types of anomalies; agenesis of corpus callosum, ventricular dilatation and cerebral matter alterations were the most frequent findings. The authors give a brief description of the clinical reports and of the anomalies observed with MRI; they conclude that MRI seems to be a valuable tool especially for the study of the alterations of the cerebral matter and their correlation with mental retardation.