We report a rare case of obstruction of the cerebrospinal fluid (CSF) pathway caused by a dilated anterior longitudinal epidural venous plexus in a 32-year-old man. The patient had a history of multiple cyst-peritoneal shunting procedures for a large posterior fossa arachnoid cyst and had been troubled by gait disturbance and clumsiness of the fingers. MR revealed T2 prolongation and swelling of the upper cervical cord and stenosis of the spinal canal due to a well-developed anterior longitudinal epidural venous plexus. Cerebral angiography revealed anomalous venous drainage of the posterior fossa and cranio-cervical junction. Internal jugular veins were not seen, but a well-developed anterior longitudinal epidural venous plexus was apparent. The cervical canal was narrowed by the dilated venous plexus and a myelopathic change of the upper cervical cord was noticed. The patient underwent C2 laminoplasty and fenestration of the cyst. In addition to describing this patient's specific case, we discuss the pathophysiology of this disease in general.