An observational cross-sectional study was carried out with the aim of determining associations between quality of sleep and harmful oral habits among children aged three to six years. This study was conducted in compliance with the Brazilian National Health Council/Ministry of Health guidelines contained in Resolution 196/96 and received approval from the Human Research Ethics Committee of the Universidade Metropolitana de Santos (Brazil) under process number 026/2010. Parents/guardians of all participants were properly informed regarding the objectives of the study and signed a statement of informed consent.