A case of a patient with multiple myelomatosis that presented diffuse leptomeningeal involvement by metastatic tissue is reported. The diagnosis was based upon necroscopic examination. The leptomeninges were infiltrated by neoplastic cells, the infiltration being more evident in the leptomeninges of the spinal canal. In this region the subarachnoid space was filled by neoplastic tissue that surrounded the spinal cord and cauda equina. The lumbal and sacral portions of spinal cord were invaded by tumor cells. Fever, congestion of left eye and signs of leptomeningeal irritation appeared at first and were followed by crural paraplegia about two months later. At this occasion a CSF examination showed changes proper to subacute inflammatory process and the manometric test of Stookey suggested the occurence of blockage in the spinal canal. The unusual leptomeningeal involvement in multiple myelomatosis is emphasized and CSF changes are discussed. It was not possible to conclude the histochemical studies of plasma cells in the necropsy material.