The following case is reported because of its intrinsic interest and the rarity of the condition, and as a possible aid in the future recognition and successful treatment of this disease. The original description of the condition is credited to Lhermitte and Duclos,1 their paper appearing in 1920. Four cases have been reported since that time, 1 each by Schmidt,2 Bielschowsky and Simon,3 Barten4 and Heinlein and Falkenberg.5 In all cases, the patient exhibited signs and symptoms of an intracranial growth, and in each case an extensive area of hypertrophied cerebellar gyri was discovered. The abnormal areas were characterized microscopically by enlargement of the nerve cells, little or no reaction of the glia and myelination of the molecular layer. None of these patients was treated successfully, but Christensen6 described a similar condition in which the patient was living and well one and one-half years