Posterior crossbite is a condition in which one or more teeth are positioned buccally or lingually with respect to the opposing posterior teeth. This relationship often co-occurs with maxillary constriction, which can be corrected with rapid maxillary expansion during the growth period. This case report describes a diagnostic approach to a class II malocclusion with posterior crossbite and treatment using a bonded HYRAX appliance. The article thoroughly explains the appliance construction, activation, and stabilization. The psychological advantages and treatment outcomes of the HYRAX appliance clearly demonstrate the benefits of early treatment.