Behcet's disease is a recurrent inflammatory disorder that affects several systems besides skin and eye. It is known that the disease may show an onset with neurological involvement. We report a 37-year-old woman who had acute onset of left internuclear ophthalmoplegia, which resulted from an ischemic lesion at midbrain, with a long-lasting history of oral aphthae and genital ulceration. The laboratory workup revealed no pathology suggesting any other disease thought of in differential diagnosis. The patient was treated with high-dose methylprednisolone and colchicine and showed marked improvement. This case is presented because it is relatively rare for Behcet's disease to affect the tegmentum of the brainstem where the medial longitudinal fibers are located.