Characteristics of oculomotor disorders of a family with Joseph's disease. The oculomotor abnormalities of 12 patients of a large Japanese family with Joseph's disease were investigated and compared with those of 27 patients with olivopontocerebellar atrophy (OPCA). All 12 patients had limitation of upward gaze, impairment of convergence and horizontal gaze nystagmus. However, none had abnormalities of pupillary shape or light reflexes. Impairments of saccadic and pursuit eye movements were frequently present. Further, difficulty of eyelid opening, bulging eyes, impairment of optokinetic and caloric responses and square wave jerks were seen in some of the patients. The autopsy examination of 1 patient revealed marked neuronal loss in the oculomotor nucleus with preservation of the Edinger-Westphal nucleus and neuronal decrease, myelin loss and gliosis of the dorsal midbrain including superior colliculus, pretectum and posterior commissures. Disturbance of upward gaze, sparing of pupillary light reflexes and horizontal gaze nystagmus were frequent and early symptoms. The pattern of oculomotor disturbances is different from that of OPCA and evaluation of the oculomotor system is useful for clinical diagnosis of the disease. 