The objective of this research was to evaluate the reliability of 2 methods (Andrews' Element III analysis and Yonsei transverse analysis) in maxillary transverse deficiency diagnosis. Plaster casts and cone-beam computed tomography images of 80 outpatients with skeletal Class I malocclusion (29 males and 51 females, mean age, 20.16±8.22years) were selected. Maxillary and mandibular width were measured, respectively, and independently by 2 examiners at an interval of 2weeks, using Andrews' Element III analysis and Yonsei transverse analysis. Intraclass correlation coefficients and Bland-Altman plots of intraexaminer and interexaminer reliability were evaluated. After diagnosis, Cohen's kappa statistics were calculated to evaluate the diagnostic agreement. The intraclass correlation coefficients were all above 0.85, indicating good to excellent reliability. Compared with Andrews' Element III analysis, Yonsei transverse analysis had higher intraexaminer and interexaminer reliability in both maxillary and mandibular width measurements. Thirty-one to 42 of the patients were diagnosed with maxillary transverse deficiency by 2 examiners using 2 methods. The intraexaminer and interexaminer Cohen's kappa values of Yonsei transverse analysis were all higher than those of Andrews' Element III analysis. Both Andrews' Element III analysis and Yonsei transverse analysis had good to excellent reliability and substantial diagnostic agreement. Yonsei transverse analysis had higher reliability in maxillary and mandibular width measurements and higher diagnostic agreement, compared with Andrews' Element III analysis.