Medulloblastoma is one of the most common primary tumors of the central nervous system of children but it is uncommon in adult age. We report a case of young male presented with a history of generalized headache that was found to have medulloblastoma with diffuse leptomeningeal involvement without prominent mass lesion. To our knowledge, our patient is the second reported case of medulloblastoma in adults identified with primary leptomeningeal involvement without a prominent mass lesion. The clinical, radiological and pathologic features of this entity are described.