The aim of this study was to evaluate the degree of abrasion in posterior teeth of subjects with unilateral posterior crossbite in the deciduous dentition. A group of 54 untreated subjects in deciduous dentition (test group, TG) was selected from a parent sample of 1500 patients from the files of the Department of Orthodontics of the University of Florence. A sample of 20 subjects with normal occlusion in the deciduous dentition was selected as the control group (CG). As experimental units in TG, 54 crossbite sides (CB, consisting of 33 right and 21 left crossbite sides) and 54 noncrossbite sides (NCB) were used. In CG, one randomly chosen single side for each subject (NCBC) was used for comparisons. The findings of the present study indicated that subjects with unilateral crossbite in the deciduous dentition showed a significantly smaller degree of dental abrasion in the crossbite side when compared with both the opposite side and control group sides. The lack of abrasion in crossbite sides was primarily due to a significantly lesser degree of abrasion of the upper deciduous canines.