Authors report one case of intravertebral vacuum phenomenon associated with a multiple myeloma. Initially, there occurred a collapse and a lysis of the L4 vertebral body. Two months later, after chemotherapy and cobalt-therapy, X-ray examination showed a vacuum cleft phenomenon within the body of L4 and a backward displacement of the L4 posterior wall. At the same time the patient complained of a cruralgia. Recovery occurred after decompression surgery. Histologic sampling of the L4 vertebral body revealed bone necrosis without any abnormal plasmocytosis. Authors draw attention to the neurological complications occurring in the course of the vertebral necrosis and to the fact that, even in case of multiple myeloma, the occurrence of a transverse vacuum cleft may result from osteonecrosis.