Rosenthal fibers are present in several neurologic disorders. Their occurrence in widespread subependymal, subpial, and perivascular locations is thought to be diagnostic of Alexander's disease, but they have also been reported in rare adult cases. Some of these patients were neurologically intact with severe systemic illnesses. In symptomatic cases, the neurologic disorder has simulated multiple sclerosis. We report an elderly woman with progressive parkinsonism, dementia, and hallucinations whose brain showed severe Rosenthal fiber proliferation.