A 68-year-old woman presented with an 18-month history of low back pain followed by leg weakness, dementia, and incontinence. Myelography revealed an intradural, extramedullary block from L-2 to L-4, and cranial computed tomography demonstrated ventriculomegaly. Excision of a benign schwannoma resulted in rapid relief of back pain and more gradual normalization of mental function and hydrocephalus. Five similar cases of dementia and hydrocephalus complicating spinal cord tumor have been reported. A variety of mechanisms have been proposed to explain the association but the pathophysiology is still unclear. Spinal tumor should be considered in the differential diagnosis of dementia and of communicating hydrocephalus.