MR imaging of the craniovertebral junction, cranium, and brain was performed in 10 patients (aged 3 months to 16 years) with achondroplasia. All patients had narrowing of the subarachnoid space at the level of the foramen magnum and five had compressive deformities of the cervicomedullary junction. Apparent upward displacement of the brainstem and a relatively vertical course of the optic nerve were seen in all patients. Dilated lateral and third ventricles were seen in five patients and bifrontal widening of the subarachnoid space was evident in four. Skull asymmetry was seen in two patients and an empty sella (confirmed by metrizamide cisternography) was present in one individual. In one patient, foci of abnormal signal intensity were seen in the cervicomedullary region. Our experience indicates that MR imaging is useful in delineating the many abnormalities of the cranial, cerebral, and cervicomedullary junction present in children with achondroplasia.