Objective: To investigate the predictive association between preschool childcare arrangements and overweight/obesity in childhood. Study design: Children were enrolled in a prospective birth cohort in Quebec, Canada (n = 1649). Information about childcare obtained via questionnaires to the mothers at ages 1.5, 2.5, 3.5, and 4 years was used to compute a main childcare arrangement exposure variable (center-based/family-based/care by a relative/nanny). Body mass index was derived from measured weights and heights at ages 4, 6, 7, 8, and 10 years and children were classified as overweight/obese versus normal weight. Generalized estimating equations were used to model the effect of main childcare arrangement (center-based/family-based/relative/nanny) (vs parental care) on overweight/obesity adjusting for several potential confounding factors. Results: Compared with parental care, children who attended a center-based childcare (OR: 1.65, 95% CI: 1.13-2.41) or were cared for by a relative (OR: 1.50; 95% CI: 0.95-2.38, although with greater uncertainty) had higher odds of being overweight/obese in childhood (4-10 years). Analyses of number of hours additionally suggested that each increment of 5 hours spent in either center-based or relative childcare increased the odds of overweight/obesity in the first decade of life by 9%. Associations were not explained by a wide range of confounding factors, including socioeconomic position, breastfeeding, maternal employment, and maternal body mass index. Conclusion: Overweight/obesity was more frequently observed in children who received non-parental care in center-based settings or care by a relative other than the parent. "Obesogeonic" features of these childcare arrangements should be investigated in future studies. (author abstract)