Introduction: Oral habits interfere in the development of the functions of the stomatognathic system; there- fore, they are an etiological factor in the development of malocclusions.   Aim: To compare the frequency of oral habits and its relationship with malocclusion in children aged 4-12 in San Luis Potosí-Mexico and Medellín-Colombia.   Materials and methods: Cross-sectional, descriptive study. Convenience sample of 598 children from 4 to 12 years old (299 children per city). For data analysis, a contingency table with chi-square was prepared using spss v. 21.   Results: The most frequent oral habit for the total sample was onychophagy. When comparing the sample in both cities, onychophagy was highly frequent in San Luis Potosí, while mouth breathing was more com- mon in Medellín. In San Luis Potosí, most children with some habit had a class i molar ratio, except those with atypical swallowing, who exhibited class iii malocclusion. From the statistical point of view, atypical swallowing was the habit with the highest significance in relation to the presence of malocclusions in the total sample. A direct relationship between the presence of posterior cross bite and digit sucking in San Luis Potosí (p ≤ 0.05) was also found.   Conclusions: Atypical swallowing and open bite are directly related, which suggests that the swallowing function can be a causal factor of malocclusion; moreover, a direct relationship between digit sucking and posterior cross bite was found