Abstract: Objective:To observe the CT imaging findings of patients with sacroiliac joint (SIJ) lesions of SAPHO syndrome and to improve our understanding of the disease. Methods:Thirty-five patients with SAPHO syndrome and SIJ involvement evidenced by bone scintigraphy were recruited. The 1984 revision of modified NewYork (mNY) criteria was used to evaluate SIJs on CT in patients with sacroiliitis. The clinical data, the distribution and degree of lesions involved SIJ were evaluated. Results:All the 35 patients exhibited abnormalities in the SIJ on CT. Among these patients, 80.0% (28/35) patients were involved bilaterally and 20.0% (7/35) unilaterally. The lesions were detected mainly in the iliac in 61.4% (43/70) patients and in the sacrum in 8.51% (6/70) patients. Both the iliac and the sacrum were equally involved were 10.0% (7/70). 92.9% (65/70) patients were involved in the anteroinferior synovial membrane, and 47.14% (33/70) patients in the posterosuperior ligament. Grade I to IV were 11.40% (4/35), 17.1% (6/35) 65.7% (23/35) 5.7% (2/35) respectively. Distribution of lesions in the upper/lower iliac bone and upper/lower sacrum were no statistical difference (P>0.05). Conclusion:SIJs are usually bilaterally involved in SAPHO patients, with a predilection for iliac synovial membrane. CT manifestations are characterized by the destruction in the early stage, and osteosclerosis in the mid-later stage, with a low prevalence of ankylosis. These CT features may be new diagnostic clues for SAPHO syndrome.