Introduction: Molar Incisor Hypomineralization (MIH) is described as a qualitative enamel development defect that affects at least one permanent molar and may or may not affect the permanent incisors. The prevalence reported in the world literature ranges from 2.8% to 44%. Its etiology is still unclear, with prenatal, perinatal and postnatal factors often associated. Objectives: evaluate the prevalence of HMI in patients attented at a Dental School in the city of Vitória-ES and its association with causal factors. Methods: 302 children aged between 5 and 14 years were clinically evaluated under ideal conditions at the Children's Clinic of the Faculty of Dentistry of MULTIVIX and a questionnaire was applied. Results: 66 children (21.85%) had HMI. There was no significant difference between the sexes and there was no association with childhood respiratory diseases and preterm birth. Conclusion: High prevalence of MIH was found in Brazilian children and no association with respiratory diseases or premature births. It is suggested that further studies be carried out with standardized criteria to determine the prevalence and its relationship with causal factors.