Purpose: To assess the impact of early childhood caries (ECC) and its clinical conse- quences on preschool children's sleep, as reported by caregivers. Methods: A representative cross-sectional study was carried out with preschoolers aged four to six years in Brazil. Caregivers responded to the Brazilian version of the Early Childhood Oral Health Impact Scale and a specific question from this questionnaire was used to determine sleep-related quality of life: "Has your child had trouble sleeping because of dental problems or dental treatments?" Additionally, a self-administered questionnaire with socioeconomic questions was used. Clinical examinations were performed by two calibrated dentists to diagnose dental caries (International Caries Detection and Assessment System -epi) and its clinical consequences (pulpal involvement, tissue ulceration, fistula and abscesses [pufa] index). Adjusted and unadjusted Poisson regression was used for data analysis (P<0.05). Results: The sample consisted of 533 preschoolers, with 259 girls (51.4 percent) (n=259). The mean age of preschoolers was 4.78±0.6 (standard deviation) years. One-third (n=176) exhibited extensive carious lesions, and 14.1 percent (n=75) had clinical consequences of ECC. Conclusion: Children with clinical consequences of ECC were approximately 3.04 times more likely to have difficulty sleeping than children without them (95 percent confidence interval=1.75 to 5.25). The clinical consequences of ECC were significantly associated with difficulty sleeping among preschool children.