The objective of the current study was to characterize the internal nasal dimensions of children with repaired cleft lip and palate and transverse maxillary deficiency, using acoustic rhinometry and analyze the changes caused by rapid maxillary expansion (RME). A convenience sampling of 19 cleft lip and palate individuals, aged 14 to 18 years, of both sexes, previously submitted to primary surgeries and referred for RME were analyzed prospectively at the Hospital for Rehabilitation of Craniofacial Anomalies, University of São Paulo, Bauru, São Paulo, Brazil. All patients underwent acoustic rhinometry before installation of the expansor and at 30 and 180 days after the active expansion phase. Nasal cross-sectional areas and volumes corresponding to the nasal valve (CSA1 and V1) and the turbinates (CSA2, CSA3, and V2) regions were determined before and after nasal decongestion. Rapid maxillary expansion led to a statistically significant increase (P < 0.05) in mean CSA1, CSA2, V1, and V2 (without nasal decongestion) and in CSA1 and V1 (with decongestion) in the group as a whole. Individual data analysis showed that 58% of the patients responded positively to RME, with an average increase in CSA1 of 26% (with decongestion), whereas 37% of the patients had no significant change. Only 1 patient (5%) showed a decrease. The findings contribute toward the characterization of nasal deformities determined by the cleft and demonstrate the positive effect RME had on nasal morphophysiology in a significant number of the patients who underwent this procedure.