Background: Previous studies have found an association between early entry to childcare and risk for overweight and obesity at 3 years of age. These studies, however, have been conducted primarily with higher income White populations or have found increased risk in the children of educated mothers. Objective: To assess the relationship between timing of entry to childcare and duration of childcare and pediatric overweight and obesity in a high risk population. Methods: Using data from a longitudinal cohort of low-income Latino children in San Francisco, we evaluated the association between time of entry to childcare, hours in childcare, and risk for overweight and obesity at age 4. Similarly, we evaluated the relationship between these same childcare parameters and body mass index Z score and risk of having a waist circumference (WC) percentile less than 90th at 4 years of age. Results: In contrast with previous studies, we found no association between being in childcare at 4 years of age or number of hours per week in childcare and risk for childhood overweight, obesity or WC less than 90th percentile at age 4. Additionally, we found no association between age of entry to childcare (6 months- 12 months of age) with risk for overweight or obesity at age 4. Future studies need to further evaluate the differential impact of childcare on early childhood obesity in relation to race/ethnicity and lower socioeconomic status. Conclusion: Low-income children may not be at increased risk for obesity in relation to early childcare exposure. (author abstract)