Introduction: The initial surgical treatment of children with cleft lip and palate often triggers centripetal deviation of the perimaxillary tissues that lead to the appearance of malocclusion. The most frequent is posterior crossbite due to maxillary constriction. Objective: The aim of this study was to evaluate the efficacy of the Quad-helix appliance in the expansion of the maxilla of patients with cleft lip and palate. Materials and Method: The study sample included 20 patients with cleft lip and palate. A pre- and post-treatment cone-beam computed tomography (CBCT) image was taken, and a superimposition of the images, using the cranial base as reference, was done. Frontal sections were used to measure maxillary transverse dimensions and teeth inclinations. Paired t-tests at a 5% level of significance were used. Results: The Quad-helix appliance showed a greater expansion in the anterior maxillary region. Expansion also produced buccal tipping of molars, premolars and deciduous first molars. Discussion: The total expansion achieved with this appliance can be divided into 3 parts: skeletal expansion, alveolar expansion and dental tipping.. It was observed that the Quad-helix produces greater dento-alveolar expansion than skeletal, probably due to the resistance of scar tissue existing in the cleft region. Conclusion: In this study it was possible to verify the efficacy of Quad-helix in transversal maxillary expansion in children with cleft lip and palate. It was also possible to verify a greater efficacy in the anterior region than in the posterior region of the maxilla with a bigger dento-alveolar component. Clinical Implications: The use of Quad-helix appliance in mixed dentition is an effective treatment in the correction of maxillary transverse discrepancy of patients with cleft lip and palate, especially when most of the maxillary collapse is in the anterior region. Schlagwörter: cleft palate, crossbite, maxillary expansion