Calcification of the posterior longitudinal ligament occurs in about 3% of adults in Japan, and in about 0.7% of hospitalized adults with spinal symptoms in the United States. The condition may be asymptomatic, however, in patients with a stenotic spinal canal or when the calcification is large, it may cause compression of the spinal cord and myelopathy. The radiographic diagnosis is made when a band of calcification is noted in the spinal canal directly posterior to the vertebral bodies. Lateral tomograms of the spine are helpful for detection and measurement of the exact thickness of the calcification. Computed tomography is particularly helpful because it reveals the thickness and the extent of lateral extension of the calcification, as well as the size of the spinal canal and the extent of its narrowing by the calcification. Seventeen patients evaluated by computed tomography are reported.