To determine whether asymptomatic spinal cord compression affects surgical outcome for another compression, we retrospectively reviewed the outcome for thoracic myelopathy due to spinal ligament ossification. Improvement assessed by changes in motor function of the lower extremity using the Japanese Orthopedic Association Classification was significantly less in cases associated with asymptomatic cervical ligament ossification (C+T group, N = 5) than in cases without cervical ligament ossification (T group, N = 13) (p < 0.05, Mann- Whitney U test). The "no disability" recovery rate was 61.5% in the T group and none in the C+T group (p < 0.05, Fisher's exact probability test). There was no significant difference in background parameters between the two groups. This study showed that concomitant spinal cord compression, even if asymptomatic itself, can adversely affect surgical outcome at a separate segment.