Objective: To investigate the prevalence of morphological and attachment variations of the maxillary labial frenum (MLF) and associated factors in preschool children. Study Design: A cross-sectional study was conducted with 1,313 children aged between zero and five years of age attending public nurseries in the city of Canoas in southern Brazil. Data were collected through a questionnaire addressing demographic, socioeconomic, and behavioral characteristics and a clinical examination of the MLF. Assessments of MLF morphology and attachment were based on the classification systems proposed by Sewerin and Mirko et al., respectively. Results: The most prevalent patterns were simple MLF (63.8%) and gingival attachment (51.1%). Morphological abnormalities were found in 21.6% of the preschoolers and 25.4% exhibited abnormal frenal attachment. Abnormalities in MLF morphology were more prevalent among girls (p = 0.003) and a significant reduction was found with the increase in age (p < 0.001). Attachment abnormalities were significantly more prevalent among girls (p < 0.001), the white ethnic group (p = 0.005), and children who used a pacifier (p = 0.007) and also reduced significantly with the increase in age (p < 0.001). Conclusion: Demographic and behavioral characteristics were associated with MLF morphology and attachment. The reduction in the prevalence of the outcomes with the increase in age suggests that surgical interventions in the first years of life may constitute overtreatment.