We report a case of Lhermitte-Duclos disease (dysplastic gangliocytoma of the cerebellum), an uncommon disorder of uncertain pathogenesis characterized by disarrangement of the normal cerebellar laminar cytoarchitecture. A 40-year-old man was admitted because of vomiting and syncope of a few days' duration, and a 2-month history of intermittent headaches and unsteady gait. A computed tomographic scan of the patient's head showed obstructive hydrocephalus due to displacement of the fourth ventricle by a large, nonenhancing cerebellar mass. The magnetic resonance images of the brain also revealed a space-occupying lesion within the right cerebellum with unusual septation. After surgery, the histologic examination confirmed the diagnosis of Lhermitte-Duclos disease. This is the first report of Lhermitte-Duclos disease in Taiwan.