Objectives:To investigate the relationship between coronoid process hyperplasia(CPH)and temporomandibular joint ankylosis(TMJA) and to analyze its pathologic mechanism and clinical meaning.Methods:28 patients with TMJA from 1984 to 2004 were retrospectively studied.The length of coronoid process and the mouth-opening degree were measured on their depicting map of panoramic radiographs.106 subjects with normal TMJ were enrolled as the controls.The relationship between CPH and case history of TMJA was statistically analysed.Results:Coronoid process in TMJA subjects was longer than that in the controls(P