Although rheumatoid involvement of the lumbar spine is relatively rare, we report a patient with rapidly progressing cauda equina symptoms due to rheumatoid diskitis. A 72-year-old woman was admitted to our hospital because of motor weakness below the iliopsoas muscle and sensory disturbance beneath the level of L2. Plain X-ray films, computed tomography, and magnetic resonance imaging demonstrated destruction of the L2/3 intervertebral disc and endplates with subluxation of the facet joints. The dural sac was compressed. Based on a diagnosis of spinal canal stenosis due to rheumatoid diskitis, we performed partial laminectomy and posterolateral fusion with pedicle screws. The neurological deficits improved immediately. The mechanism of intervertebral disc destruction in this case is thought to be rheumatoid nodes or enthesitis. Destruction of the facet joints and the intervertebral disc might have led to severe instability and spinal canal stenosis.