The aim of this longitudinal study was to assess whether correction of unilateral posterior cross bite in the primary dentition results in improvement of facial symmetry and increase of palatal surface area and palatal volume. A.group of 60 Caucasian children in the primary dentition, aged 5.3 ± 0.7 years, were collected at baseline. The group consisted of 30 children with a unilateral posterior cross bite with midline deviation of at least 2 mm (CB) and 30 without malocclusion (NCB). The CB group was treated using an acrylic plate expander. The children ' s faces and dental casts were scanned using a three-dimensional laser scanning device. Non- parametric tests were used for data analysis to assess differences over the 30 months period of follow-up. The CB children had statistically signifi cantly greater facial asymmetry in the lower part of the face ( P.< 0.05) and a signifi cantly smaller palatal volume ( P.< 0.05) than the NCB children at baseline. There were no statistically signifi cant differences between the two groups at 6, 12, 18 , and 30 months follow-ups. Treatment of unilateral posterior cross bite in the primary dentition period resulted in an improvement of facial symmetry in the lower part of the face ( P.< 0.05) and increase of the palatal surface area and palatal volume ( P.< 0.001). At 30 months, relapse was observed in eight children (26.7 per cent). Treatment of unilateral posterior cross bite in the primary dentition improves facial symmetry and increases the palatal surface area and the palatal volume, though it creates normal conditions for normal occlusal development and skeletal growth. © The Author 2011.