Class II malocclusion is a common clinical problem among white Caucasian population and its transverse component is a critical aspect of a functional and stable occlusion. The size and shape of the arches have considerable implications in orthodontic diagnosis and treatment planning, affecting the space available, dental esthetics, and stability of the dentition. Hence , it is important to study the alveolar arch width in this group of patients using the wide possibilities of cone beam computed tomography of evaluating real anatomy , true-to-scale images without distortions or superimpositions, and the selection of the desired sections.Objective:To evaluate the width of maxillary and mandibular alveolar arches in skelatal Class II adults compared to skeletal class I using cone beam computed tomography. Materials and methods: thirty-two subjects with skeletal Class II relationship and 10 subjects with skeletal Class I who were ordinary undergoing CBCT scan for non-orthodontics nor for otorihnolaryngology purpose were selected to measure the maxillary and mandibular alveolar width of first premolar and first molars.Independent samples’ t-test was calculated. Results:No statistically significant differences were found of alveolar widths between skeletal Class II and Class I subjects in both maxillary and mandibular widths of molar and premolar regions. Gender had no statistically significant effect in the results of the study. Conclusion :There is no differences in alveolar width between adults with skeletal Class II and Class I relationships, so the transverse discrepancy in skeletal Class II when exsists , it is more probably not originated from the alveolar base.