Background: An increased prevalence of overweight and obesity for adults on government-funded nutrition assistance, such as the Supplemental Nutrition Assistance Program (SNAP), has been observed; however, this association among preschool-aged children is not well understood. Longitudinal research designs tracking changes in body mass index-for-age (BMI) in children of low-income households may provide a clearer picture of the association between SNAP participation and overweight and obesity among this age group. To determine if there is a relationship between SNAP participation and overweight and obesity prevalence in low-income, preschool children, we conducted a cross-sectional analysis of children in a Head Start program, and a longitudinal analysis of those children who were enrolled for 2 years. Methods: Height and weight data and SNAP participation of 386 students (207 male, 179 female, 4.2 [plus or minus] 0.5 years) enrolled in a Head Start program were analyzed; data for 2 years were available for 167 of the students. Height and weight measures were used to determine BMI percentile per Centers for Disease Control and Prevention guidelines. SNAP participation was obtained through a nutritional questionnaire given to parents at time of Head Start Program enrollment. Results: No significant differences were found between SNAP and non-SNAP participants for BMI percentile in either the cross-sectional or longitudinal analysis. BMI percentile increased for both groups over time, but failed to reach significance (p = 0.13). Conclusion: Future studies are warranted with an inclusion of a larger and more geographically diverse sample to further determine the association between SNAP participation and overweight and obesity in preschool-aged children. (Contains 2 tables and 2 figures.)