Background: Physical activity, sedentary behavior, and sleep are all movement behaviors that range on a continuum from no or low movement, to high movement. Consistent associations between movement behaviors and adiposity indicators have been observed in school-age children. However, limited information exists in younger children. Since approximately 50 % of Canadian children [less than or equal to] 5 years of age attend non-parental care, movement behaviors within and outside of the child care setting are important to consider. Therefore, this study examined the association between movement behaviors (physical activity, sedentary behavior and sleep) inside and outside of child care, with body mass index (BMI) z-scores, among a sample of toddlers and preschoolers. Methods: Children aged 19-60 months (n = 100) from eight participating child care centers throughout Alberta, Canada participated. Movement behaviors inside child care were accelerometer-derived (light physical activity, moderate to vigorous physical activity (MVPA), sedentary time, and time spent in sedentary bouts lasting 1-4, 5-9, 10-14 and [greater than or equal to]15 min) and questionnaire-derived (daytime sleep). Movement behaviors outside of child care were questionnaire-derived (MVPA, screen and non-screen sedentary behavior, and nighttime sleep). Demographic information (child age, child sex, and parental education) was also questionnaire-derived. Height and weight were measured, and age- and sex-specific BMI z-scores were calculated using World Health Organization growth standards. The association between movement behaviors and BMI z-scores were examined using linear regression models. Results: Hours/day of sedentary bouts lasting 1-4 min ([beta] =-0.8, 95 % CI:-1.5,-0.1) and nighttime sleep ([beta] = 0.2, 95 % CI: 0.1, 0.4) were associated with BMI z-scores. However, after adjusting for demographics variables, sedentary bouts lasting 1-4 min ([beta] =-0.7; 95 % CI:-1.5, 0.0) became borderline non-significant, while nighttime sleep ([beta] = 0.2, 95 % CI: 0.1, 0.4) remained significant. No other movement behaviors inside/outside of child care were associated with BMI z-scores. Conclusions: All children must engage in some sedentary behavior in a day, but promoting the sedentary behavior in short bouts during child care may be important for the primary prevention of overweight and obesity. Future research is needed to understand the mechanisms between sleep and adiposity in this age group and to confirm these findings in large representative samples. (author abstract)