Introduction: The present study investigates the relationship between respiratory patterns and mandibular morphology. Methods: The study sample comprised 100 pre-orthodontic patients ranging from 8 to 13 years of age. The subject sample was evaluated by clinical examination and lateral cephalometric radiographs. A clinical examination of respiratory patterns categorized the subjects as mouth breathers (Group M, n=52) and nasal breathers (Group N, n=48). Results: The Student t test revealed a statistically significant relationship (p<0.05) between Group M and deep antegonial notch and greater lower anterior facial height. Conclusions: The results of this study suggest that deep mandibular antegonial notch and vertically directed growth pattern are more prominent in individuals who are mouth breathers.