Downbeating nystagmus is an involuntary vertical rhythmic eye movement with the fast component in the downward direction. The sign indicates a craniocervical disorder. The most common cause is the Arnold-Chiari malformation, followed by cerebellar degeneration. Basilar invagination is a rare cause of downbeating nystagmus. However, with appropriate treatment its prognosis is good. Here, we report a case of basilar invagination which presented with downbeating nystagmus and postural hypotension. A 31 year-old Thai male patient had a 20 year history of postural hypotension. He had recurrent pneumonia and cough-induced syncope a year before admission. He complained of symptoms of an acute febrile illness and a productive cough. The physical examination showed high grade fever, postural hypotension and medium crepitation in the right upper lobe. The neurological examination showed downbeating nystagmus, atrophy and fasciculation of the right side of the tongue, atrophy of the right sternocleidomastoid muscle, mild weakness of the extremities and generalized hyperreflexia. The cervical spine X-ray revealed upward displacement of the vertebral bodies of C1 and C2, with a mild narrowing of the space between C1 and the occiput. The CT-myelogram and MRI showed upward displacement of C1 with overriding of the dens over the anterior lip of the foramen magnum; this also compressed the medulla. Syringomyelia was seen at the C1-C5 level. We report a patient who presented with postural hypotension, recurrent pneumonia and downbeating nystagmus due to basilar invagination. The symptoms were aggravated by cough which caused an increase in intracranial pressure. This resulted from medulla compression in the foramen magnum by the first cervical spine. The treatment of choice was surgical decompression.