Sleep is a vital physiological function for the maintenance of health and quality of life. Harmful, non-nutritive and parafunctional oral habits are believed to have a negative effect on adequate rest at night. The aim of the present study was to determine associations between quality of sleep and harmful oral habits among children aged three to six years. Fifty children from a private school in São Paulo (Brazil) were evaluated using two questionnaires on sleep quality and harmful oral habits. The data were submitted to descriptive analysis. The chi-square test was employed for the categorical variables and analysis of variance (ANOVA) was carried out to compare mean values. The Student's t-test was used for all analyses, with the significance level set at 5%. The SPSS 12.0 program for Windows was used to analyze the results.