BACKGROUND This retrospective study was designed to investigate the position changes and movement patterns of incisors and molars after orthodontic treatment with extractions of 4 second premolars in patients with mild crowding, slight dental protrusion, and Angle Class I relationship. METHODS Pretreatment and posttreatment cephalograms of 26 subjects were chosen from patients treated by an experienced orthodontist. The movements of the incisors and the molars as well as tooth tipping were measured. RESULTS Relative to the posttreatment occlusal plane, the mean incisor movements were 3.3 and 2.9 mm lingually in the maxilla and the mandible, respectively. The first molars were moved mesially an average of 3.2 and 3.4 mm in the maxilla and the mandible, respectively. The incisor inclination was under proper control. The extraction space was almost equally taken up by the anterior and posterior segments. CONCLUSIONS These data can be used to estimate the expected position changes and movement patterns of the incisors and molars in patients with mild crowding and slight bialveolar dental protrusion after orthodontic treatment with 4 second premolar extractions.