Objective: To quantitatively evaluate the effects of asymmetric rapid maxillary expansion (ARME) on cortical bone thickness and buccal alveolar bone height (BABH), and to determine the formation of dehiscence and fenestration in the alveolar bone surrounding the posterior teeth, using conebeam computed tomography (CBCT). Materials and Methods: The CBCT records of 23 patients with true unilateral posterior skeletal crossbite (10 boys, 14.06 ± 1.08 years old, and 13 girls, 13.64 ± 1.32 years old) who had undergone ARME were selected from our clinic archives. The bonded acrylic ARME appliance, including an occlusal stopper, was used on all patients. CBCT records had been taken before ARME (T1) and after the 3-month retention period (T2). Axial slices of the CBCT images at 3 vertical levels were used to evaluate the buccal and palatal aspects of the canines, first and second premolars, and first molars. Paired samples and independent sample t-tests were used for statistical comparison. Results: The results suggest that buccal cortical bone thickness of the affected side was significantly more affected by the expansion than was the unaffected side (P <.05). ARME significantly reduced the BABH of the canines (P <.01) and the first and second premolars (P <.05) on the affected side. ARME also increased the incidence of dehiscence and fenestration on the affected side. Conclusions: ARME may quantitatively decrease buccal cortical bone thickness and height on the affected side.