A total of 108 patients with ossification of the posterior longitudinal ligament (OPLL) (n = 92), ossification of the yellow ligament (OYL) (n = 8), or both (n = 8) were examined with magnetic resonance (MR) imaging performed with 0.5-T superconductive and 0.22-T resistive units. OPLL was demonstrated as a low-signal-intensity band between the bone marrow of the vertebral body and the dural sac on T1- and T2-weighted images. Continuous cervical OPLL was easier to diagnose than segmental cervical OPLL. T2-weighted images were more useful for detection of ossification of the ligaments. OYL was recognized as an impression on the posterior dural sac. Formation of bone marrow within an area of ossification, shown as increased or intermediate signal intensity, was observed in 56% of the cases of continuous OPLL, 11% of the cases of segmental OPLL, and none of the cases of OYL. The degree of cord compression was more severe in continuous OPLL. Degeneration of the disk was frequently associated with both types of OPLL.