Objective: The aim of this study was to determine: (1) the relationship between the sum of mesiodistal dimensions of mandibular incisors and that of mesiodistal dimensions of maxillary or mandibular canines and premolars in Vietnamese subjects; (2) the linear regression equations that serve to predict the sum of mesiodistal dimensions of canines and premolars in Vietnameses; (3) the reliability of Tanaka and Johnston's prediction formula when applying in Vietnameses compared to the linear regression equations established in this current study. Method: In this descriptive cross - sectional study, the sample consisted of 62 dental casts (36 males and 26 females aged of 15 years).