The purpose of this study was to evaluate stability of occlusion in adult cases at least 4 years after orthodontic treatment and to clarify parameters influencing this stability. The subjects were 25 cases (mean age: 19 y 8 m) who had been treated with Edgewise technique involving first-premolar extraction. During orthodontic treatment, decreases in the maxillary and mandibular incisors' irregularity index (Max.I.I. and Mand.I.I.), posterior movement of the upper and lower incisors, increases in upper incisal height, decreases in lower incisal height, and increases in upper and lower canine width were noted. In the posttreatment period, increases in Max.I.I. and Mand.I.I., anterior movement of incisors, increases in incisal height, and decreases in canine width were observed. The amounts of overjet and overbite decreased during the treatment period and increased during the post-treatment period. Multiple regression analysis was useful to deduce which parameters influenced stability of occlusion after orthodontic treatment.