A 21-year-old man with a 5-month history of diplopia caused by isolated vertical ocular misalignment had normal laboratory studies, including brain magnetic resonance imaging (MRI). Eight months after the onset of diplopia, he reported dry mouth, polydipsia, polyuria, and absent sweating. Examination now disclosed light-near dissociation of the pupillary responses, convergence-retraction nystagmus, and upgaze palsy. MRI revealed enhancing suprasellar and pretectal masses presumed to be germinomas. Two years after brain irradiation and systemic chemotherapy, no lesions are apparent on MRI and hypothalamic dysfunction has partially resolved. In a young patient with isolated vertical diplopia and normal brain imaging, one should consider an early pretectal syndrome and inquire after manifestations of hypothalamic dysfunction.