purpose: to determine the occurrence of anterior open bite and harmful oral habits in children from four to six-year old. methods: a total of 266 four-to-six-year-old male and female children in the city of suzano (s？o paulo, brazil) were evaluated. an assessment chart for detecting the occurrence of harmful oral habits was administered to the guardians and clinical exams were performed for assessing occlusion in the children. results: a total of 221 children (83.1%) had at least one harmful oral habit, the most frequent of which was the use of a feeding bottle (n=167; 75.6%). the occurrence of simultaneous harmful habits and dental occlusion abnormalities was observed in 119 children (44.1% of the sample); among these children, the greatest prevalence was of anterior open bite (n=89; 79.8%). conclusion: anterior open bite was the most prevalent occlusion alteration in the children and had a statistically significant association with harmful oral habits, such as the use of a bottle and/or pacifier and teeth grinding.