Posterior crossbite refers to inadequate transversal relationship of maxillary and mandibular teeth. Posterior crossbite can be unilateral left, unilateral right or bilateral. The causes of this malocclusion are deleterious oral habits, early loss of primary teeth, hereditary factors and environmental factors. It is important to know the prevalence of posterior crossbite in order to provide proper treatment as early as possible. Posterior crossbite when not treated early, can result in skeletal changes. The aim of the study was to assess the prevalence of posterior crossbite in children of chennai. The present study was a retrospective observational study conducted in a university dental hospital located in Chennai. Data of 7415 Pediatrics patients between June 2019-March 2020 were reviewed. Patients from 6 to 13 years who had posterior crossbite were noted. This was followed by Excel tabulation . Data analysis was done in SPSS software using Chi square test for comparison of groups. About 1.4% children visiting university dental hospitals among 4292 children had posterior crossbite. Children of 10 to 13 years had more prevalence of posterior crossbite (P=0.349, statistically not significant) and prevalence of posterior crossbite was more in boys than girls (P= 0.175, statistically not significant) .