To investigate the parameters that affect the severity of open bite, 111 cephalometric radiographs of open bite subjects were evaluated and compared to 60 cephalometric radiographs of normal controls. While all the control subjects had Class I molar relationship, the open bite group were 49% Class I, 30% Class II, and 21% Class III. Significant increase in the means of the following measurements was found in open bite subjects: the total face height, the lower face height, the Y-axis, the gonial angle, the lower occlusal plane angle, and the mandibular plane angle, while significant decrease was found in the total posterior face height, the lower posterior face height, the mandibular body length, the maxillary length, ramus height, facial angle, and interincisal angle. Parameters that correlated highly with open bite were: lower occlusal plane to SN, mandibular plane to SN, gonial angle, Y-axis, lower anterior face height. Parameters that showed significant inverse correlation with open bite were: ramus height, maxillary length, mandibular length, lower posterior facial height, and total posterior facial height.