The MRI findings in rostral vermian dysplasia are described for the first time. Defective foliation and abnormal fissuration of the rostral vermis can clearly be depicted on coronal images. The abnormalities are limited to the anterior lobe of the vermis and its hemisphere extension. A hypothesis is put forward to explain the abnormalities. It is suggested that the vermian changes result from an intrauterine insult at the end of the first trimester. There appears to be a variable degree of expression and associated cerebellar and cerebral cortical abnormalities can be seen. The clinical significance of these findings remains incompletely understood but may be related to the severity of the abnormalities. It is also suggested that a mild degree of vermian rostral dysplasia may represent an incidental imaging finding.