Objective To investigate the clinical significance of three-dim en sional CT in diagnosis and treatment of posterior pelvic ring fractures. Methods A retrospective analysis was done for 19 cases of posterior pelvic ring fractur es who were treated from March 2002 to August 2003 and had plain and three-dime nsional CT films. Their radiological characteristics and results were compared b etween the 2 kinds of film. Results 3-D CT corrected the misdiagnosis or uncert ainty of 9 cases who had plain radio-graphs. The 3-D CT showed obvious advanta ges over plain radio-graphs in detecting sacroiliac diastasis, sacroiliac joint fragments, fractures involving iliac and sacral lips abutting the sacroiliac jo int, sacral fracture and complicated comminuted fracture, because it clearly del ineated fractures of posterior pelvic ring and manifested the severity of commin ution and separation. Conclusion The 3-D CT scan provides valuable information for precise diagnosis and treatment plan for the complex posterior pelvic ring f ractures.