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Introduction: The nostril sill is defined as the “facial subunit composed of fibro-adipose soft tissue whose topographic delimitation is given by four anatomical limits: the medial crura of the columella on its medial limit, the nasal wing on its lateral limit, the nasal vestibule in its upper limit, and the upper lip on the lower limit.” It represents an essential element in the appearance, balance, and function of the nose. The study and classification of the nostril sill in the healthy Mexican pediatric population are the necessary tools for facial reconstruction since it is generally affected in patients with cleft lip and palate and craniofacial malformations. Objective: The objective of the study is to describe the nostril sill in the Mexican pediatric population using standardized photographs taken in frontal and basal projections and classifying according to Oh et al. and to study if there is a significant relationship between nostril sill with age and gender. Materials and Methods: An observational cross-sectional study was carried out in a sample size of 83 healthy children aged between 3 and 12 years, simple randomly chosen. The classification was performed with facial photographs in frontal and basal projections. The data analysis was performed with descriptive statistics, kappa concordance coefficient was used between observers, and bivariate analysis was used to evaluate the association of the nostril sill classification with age and gender. Results: Of the 83 volunteers, 51.8% (n = 43) were female and 48.2% (n = 40) male, with a mean age of 7.38 years. The 74.6% (n = 62) were classified as a nostril sill Type I, 14.4% (n = 12) as Type III, and 10.8% (n = 9) as Type II, with a Cohen's kappa coefficient between observers of 0.92 (almost perfect agreement). In the bivariate analysis with Chi-square test, no statistically significant association was found between age (P = 0.420) and sex (P = 0.524). Conclusion: The nostril sill of the nostril represents a fundamental nasal subunit that every reconstructive surgeon must recognize and locate. It is crucial to describe and classify the nostril sill according to ethnic and racial characteristics, in the Mexican pediatric population, the most frequent corresponds to Type I, followed by Type III and finally the least frequent Type II, and that gender and age are not associated with a specific type.