Objective: This study was designed to determine the prevalence of asymmetrical root resorption and associated factors in primary mandibular molars in children aged 3-12 years. Design: A cross-sectional study was carried out with a representative sample of 1068 molars evaluated using 671 radiographs from 453 children. Age, dental history, and medical history were recorded using a questionnaire administered to the children's parents/caregivers. Asymmetrical root resorption, dental crown status (sound, caries without pulp involvement, caries with pulp involvement, and evidence of restoration), periradicular lesion, and pulpotomy or pulpectomy were determined. Data analysis involved descriptive statistics, the Chi-square test and a multivariate logistic regression (P < 0.05). Results:The prevalence rate of asymmetrical root resorption was 3.8%. The 8-12 years age bracket (odds ratio [OR]: 5.8; 95% confi dence interval [CI]: 2.3-15.1; P < 0.001) and presence of pulpotomy (OR: 2.8; 95% CI: 1.1-7.4; P < 0.05) were predictors of the occurrence of asymmetrical root resorption in primary mandibular molars. In conclusion, the prevalence of asymmetrical root resorption was low. Conclusion: Child's age and the presence of pulpotomy were associated with a greater occurrence of this type of resorption.