ABSTRACT Purpose To verify the relationship between maximum tongue pressure and the etiology of oral breathing in oral breathing children attended at the Oral Respiratory Outpatient Clinic. Methods A descriptive and analytical cross-sectional study was accomplished with 59 mouth breathing children aged 3 to 12 years (mean age 6.5 years and SD: standard deviation= 2.4). To collect tongue pressure, the Iowa Oral Performance Instrument (IOPI) was used and data regarding the etiology of oral breathing and dental occlusion were collected in the records of these patients for analysis. The associations between the maximum tongue pressure and the etiology of oral breathing, age, gender and dental occlusion were verified by the T test, ANOVA, Spearman's coefficient and Tuckey's test, using a significance level of 5%. Results There was a moderate and positive correlation between age and maximum pressure, it was verified that there was a statistically significant difference between the maximum tongue pressure and the variables pharyngeal tonsil hypertrophy and palatine tonsil hypertrophy. There were no statistical differences between the other variables. Conclusion It was concluded that mechanical obstructions, among them the pharyngeal and palatine tonsil hypertrophy alter the maximum tongue pressure in oral breathing children.