Aim: To evaluate the prevalence of caries in primary dentition in preschoolers in Parnaíba, Brazil and identify associated factors. Material and Methods: The sample studies were children in primary dentition aged between two and six years. Both the children and their parents or guardians agreed to the child’s participation in the study. Those preschoolers with syndromes or special needs, those who did not tolerate the dental examination and those with a fixed orthodontic appliance were excluded. The questionnaire was completed by a parent or guardian of each child and the 360 children’s teeth were examined, using the International Caries Detection and Assessment System (ICDAS). The data were dichotomized as presence of cavity related to caries - caries free and non-cavitated lesions (ICDAS 0, 1 and 2) and cavitated lesions (ICDAS ≥3).The presence of early childhood caries was determined and cavitation of the carious process was evaluated. Indications for necessary extraction of any primary teeth due to the carious process were noted. Results: The prevalence of caries in our sample of two to five-year-old children was 43.3% (p<0.05), with no significant difference between ages or genders. The majority of children (84.6%) presented with caries in two or more teeth. Only 15.38% of these children had caries in a single tooth. The most commonly affected tooth was number 75, followed by teeth 55, 54 and 84. The prevalence of caries in preschoolers was found to be correlated with low socioeconomic status and poor quality of life. Conclusion: The prevalence of caries in preschool children was 43.3%. Several factors were associated with dental caries in primary dentition. Children with caries were unlikely to use dental floss or brush their tongues, were only taken for dental treatment when they experienced oral pain and had parents who did not consider brushing teeth after a meal to be important.