A case of convergence-retraction nystagmus with upward vertical gaze paralysi s and skew deviation (right hypotropia), without any other neurological signs, i s reported. The probably vascular lesion was located at the mesodiencephalic jun ction, lying between the right border of the posterior commissure, the right int erstitial nucleus of Cajal and the periaqueductal grey matter, accounting for th e three ocular motor signs. The particular interest of this case is due to the relative smallness of the lesion. A case of convergence-retraction nystagmus with upward vertical gaze paralysi s and skew deviation (right hypotropia), without any other neurological signs, is reported. The probably vascular lesion was located at the mesodiencephalic junction, lying between the right border of the posterior commissure, the right int erstitial nucleus of Cajal and the periaqueductal gray matter, accounting for th e three ocular motor signs. The particular interest of this case is due to the relative smallness of the lesion.