The case of a 60 year-old man who had an indifferenciated carcinoma in the lung is reported. He had recieved cobaltotherapy and had improved. After 3 months a lumbar pain had begun and the patient was hospitalized. A myelography with lipiodol demonstrated an intra-dural mass. At operation a big intra-dural tumor including the cauda equina was found. The microscopic examination revealed an undifferenciated carcinoma, that infiltrated the epi and peri-neural space.