Internuclear ophthalmoplegia is a conjugated gaze disorder characterized by impaired adduction on the side of a lesion involving the medial longitudinal fasciculus with dissociated nystagmus of the other abducting eye. Six patients with INO(who had clinical cerebrovascular diseases) underwent MR imaging and the results were as follows : 1. The MLF lesions were identified by MR imaging in 5 cases 2. The ratio of unilateral INO to bilateral INO was 5:1 3. The nature of lesions was infarction in 4 cases and hemorrhage in 1 case 4. The sites of MLF lesion were in the midbrain in 4 cases and in the pons in 1 case 5. All 5 cases of INO identified by MR imaging had other lesion sites in addition to MLF lesion.