To investigate the mechanism of high occurrence of cervical spondylotic myelopathy in the patients with degenerative lumbar spinal stenosis and the relationship between these two diseases.Lateral radiographic plain films were made on 68 cases with degenerative lumbar spine stenosis 23 males and 45 females, aged 50.0 (22 - 69). The sagittal diameter of the spinal canal (a) was obtained by measuring the shortest distance between the middle point of the posterior margin of the cervical spinal body to the connective cortex of spinal process and vertebral lamina, the distance between the middle points of anterior and posterior margins of vertebral body was measured as the sagittal diameter of vertebral body (b), and the ratio of these sagittal diameters was calculated for the vertebral bones C3 - C7. The data of sagittal diameters of cervical spinal canal and cervical vertebral body and relevant a/b ratio value obtained from 411 healthy subjects ware used as normal controls to be compared with those of the degenerative lumbar spine stenosis patients.In the group of degenerative lumbar spinal stenosis the average value of a/b ratio of C3 - C7 were 0.781 in the males and was 0.807 in females respectively, both significantly lower than those of the healthy control group (0.874 in the males and 0.968 in the females respectively, both P < 0.05). The incidence rate of developmental cervical spinal stenosis in the group of degenerative lumbar spine stenosis was 27.9%, and that in healthy objective was 10%.Compared to the healthy objectives, the patients with degenerative lumbar spinal stenosis is easier to be inclined to the developmental cervical spinal stenosis.