The medial longitudinal fasciculus (MLF) plays a critical role in transmitting information necessary for the coordination and synchronization of various types of eye movements. Pathological processes affecting this pathway can lead to a wide range of neuro-ophthalmological signs and symptoms (Frohman, Galetta, Fox, Solomon, Straumann, Filippi et al., Neurology 70(17):e57–67, 2008). Internuclear ophthalmoplegia (INO) is a condition caused by damage to the MLF, most frequently resulting from vascular, tumoral, or demyelinating lesions. Bilateral INO, particularly in young patients (Johkura, Kudo, Amano, Kikyo, Imazeki, Amari, et al. J Neurol Sci 353:158–60, 2015), is often associated with demyelinating diseases and constitutes a syndrome known as WEBINO (Wall-eyed binocular internuclear ophthalmoplegia), characterized by horizontal eye movement disorders. Additionally, there can be mild bilateral lesions of the MLF that do not meet the full criteria for WEBINO. However, mesencephalic INO can also be associated with vertical eye movement disorders, although this is less common. Here, we report two cases. The first case involves bilateral INO due to lesions of the MLF, accompanied by upgaze palsy resulting from damage to the MLF and pontomesencephalic vascular lesions. Additional findings included convergence–retraction nystagmus during attempted upgaze, a hallmark of dorsal midbrain (Parinaud) syndrome. The second case features mild bilateral INO as the initial presentation of multiple sclerosis in a young, otherwise healthy patient. This report highlights the anatomical structures and projections associated with the MLF and explores the spectrum of oculomotor abnormalities caused by lesions in this pathway.