Objective: To determine the impact and best management sequence between adenotonsillectomy (AT) and rapid maxillary expansion (RME) on the apnea-hypopnea index (AHI) and minimum oxygen saturation (MinSaO ₂) in non-obese pediatric obstructive sleep apnea (OSA) patients presenting relatively normal sagittal and vertical craniofacial features. Study Design/Methods: Thirty-two children with a mean age of 8.8 years, with a graded III/IV tonsillar hypertrophy and maxillary constriction, participated in a cross-over randomized controlled trial. As the first intervention, one group underwent AT while the other underwent RME. After six months, interventions were switched in those groups, but only to participants with an AHI > 1 after the first intervention. Polysomnography (PSG) was conducted before (T ₀), six months after the first (T ₁) and the second (T ₂) intervention. The influence of sex, adenotonsillar hypertrophy degree, initial AHI and MinSaO ₂ severity, and intervention sequence were evaluated using linear regression analysis. Intra- and inter-group comparisons for AHI and MinSaO ₂ were performed using ANOVA and Tukey´s test. Results: The initial AHI severity and intervention sequence (AT first) explained 94.9% of AHI improvement. AT caused more significant AHI improvements than RME. The initial MinSaO ₂ severity accounted for 83.1% of MinSaO ₂ improvement changes. Most AHI reductions and MinSaO ₂ improvements were due to AT than RME. In most cases, RME had a marginal effect on AHI and MinSaO ₂ when adjusted for confounders. Conclusions: Initial AHI severity and AT as the first intervention accounted for most of the AHI improvement. The initial MinSaO ₂ severity alone accounted for the most changes in MinSaO ₂ increase.