An undocumented criticism of extraction treatment is that it results in narrower dental arches when compared with nonextraction therapy. Anterior and posterior arch widths of the maxillary and mandibular arches of 25 patients treated by 4 first-premolar extraction and 25 patients treated without extractions were measured on posttreatment study models and compared statistically to determine whether the dental arches were narrower after extraction treatment, to test the accuracy of this view. Measurements were made in the canine and the molar regions from the most labial aspect of the buccal surfaces of the canines and the molars. In both groups, anterior and posterior arch widths were the same except for the mandibular intercanine dimension, which was 0.94 mm larger (P <.01) in the extraction group. This indicates that extraction treatment does not result in narrower dental arches than nonextraction treatment.