Objectives: To reveal the possible role and mechanism of disc-facet angle in the occurrence and progress of Hirayama disease by analyzing the correlation of clinical appearance and the variation of disc-facet angle in Hirayama disease. Methods: 45 patients with Hirayama disease treated in the orthopedic de-partment of Peking University Third Hospital from October 2006 to January 2012 were reviewed. There were 44 males(97.8%) and 1 female(2.2%) with an average age of 19.33±3.89(range 13-37) years old. The onset age was 16.33±2.73 (range 10-27) years old and the duration of history was 35.64±23.24 (range 1 to 120) months. The disc-facet angle of C3-T1 was measured on PACS system. An extension line was made along the upper edge of objective vertebral body on the CT scan sagittal reconstruction image. An extension line was made along the joint surface of upper articular process of objective vertebra on the sagittal plane which crossed the midpoint of the facets. The blunt angle between two lines was the disc-facet angle. The cases were divided into unilateral affect and bilateral affected group according to history, spinal cord function and spinal cord lesion level. The correlation of above data and the variation of disc-facet angle were analyzed. Results: The duration of history in unilateral affected patients was significantly shorter than that of bilateral affected patients (P<0.05). The duration of history in sequential onset patients was significantly shorter than that of simultaneous onset in bilateral affected patients (P<0.05). The JOA score 17 and Chinese score 40 in unilateral affected patients were higher than those of bilateral affected patients. The C3-C7 disc-facet angle of affected side was bigger than that of normal side in unilateral affected patients, and C5, C6 had statistically significant difference (P<0.05). The spinal cord lesion level was mainly at C5 and C6 in unilateral affected group. The disc-facet angle had no difference on both sides in bilateral affected patients but the figures at C4 and C5 level were bigger than that of normal side in unilateral affected patients. The spinal cord lesion level was mainly at C4 and C5 in bilateral affected group. The stability of upper cervical spine segments was even worse in unilateral affected group and resulting in higher level of spinal cord lesion comparing with bi-lateral affected group. Conclusions: The disc-facet angle of C4, C5 is bigger in bilateral affected patients and may be correlated with higher level spinal cord lesion and more severe clinical symptoms. The C5, C6 disc-facet angle of affected side is significantly bigger than that of normal side in unilateral affected patients. This may be the key factor of spinal cord lesion mainly at C5 and C6 level on the same side.