A case of mobile tumor of the cauda equina was presented with a brief review of factors relating to the mobility. A 66-year-old man was admitted to our hospital complaining of left lumbago aggravated by coughing or assuming the supine position. However, neurological examination failed to reveal any abnormalities. The initial myelography showed complete obstruction above the superior border of the L1 vertebra, while the second myelography showed the same obstruction, but it had moved upwards to the superior border of T12. Surgery revealed an elastic, soft tumor and cystic dilatation of the subarachnoid space above and below the tumor. The tumor was mobile but originated from a single elongated and tortuous nerve of the cauda equina. Pathologic examination revealed neurinoma.