BACKGROUND: Although neuroradiological findings of Möbius syndrome have been reported as a result of brain and brainstem abnormalities, magnetic resonance imaging (MRI) now permits the direct imaging of the cranial nerve (CN) and branches in the orbits. This study presents the MRI findings in patients with sporadic Möbius syndrome. METHODS: Prospectively, CNs were imaged in the cistern using head coils and three dimensional fast imaging employing steady-state acquisition (3D-FIESTA), yielding a 0.5 mm(2) resolution in planes of 0.8 mm thickness in seven patients with sporadic Möbius syndrome. The cavernous and intraorbital segment of the CN and the extraocular muscles (EOMs) were imaged with T1 weighting in all patients. The cavernous segment was imaged in coronal planes, while the intraorbit in quasicoronal planes were imaged using surface coils. Intraorbital resolution was 0.16 mm(2) within 2.0 mm thick planes. RESULTS: In the seven patients, the CN were absent or showed hypoplasia in the cistern, cavernous sinus, and orbit. Abducens (CN VI) and facial (CN VII) nerves were absent on the affected sides. Unilateral CN IX (glossopharyngeal nerve) in two cases displayed dysplasia. Branches from the inferior division of CN III were observed to innervate the lateral rectus (LR) bilaterally in three cases and unilaterally in one case, and had intimate continuity with the LR muscle in two cases bilaterally and two cases unilaterally. Hypoplasia of EOMs was shown in five cases. Dysplasia of the medulla on the left side was found in one patient. CONCLUSIONS: Direct imaging of CNs and EOMs by MRI is useful in diagnosis of Möbius syndrome. It can directly demonstrate the abnormalities of the CN and orbital structures. The absence or hypoplasia of CN VI and CN VII may be the most common radiologic features in sporadic Möbius syndrome, and hypoplasia of CN IX may be an associated feature. The abnormality of EOMs and aberrant innervations in the orbit should be observed, and may be important for the study of the etiology.