Background: Social disadvantage is associated with childrens risk of being overweight or obese, but little is known about how it impacts weight trajectory. This longitudinal analysis examines food insecurity and weight change over time among low-income children in a multidisciplinary weight management clinic. Methods: Food insecurity was assessed between 2008 and 2016 among 794 low-income patients (household income <$60k/year) who attended 3234 visits. Mixed-effects growth curve modeling was used to examine the association between baseline food security status and weight trajectory, using percentage of the 95th percentile for BMI (%BMIp95). Random effects (each childs growth curve) and fixed effects (food insecurity, starting age and %BMIp95, demographics, and months since the initial visit) were modeled, and interactions between food insecurity and elapsed time estimated the influence of food insecurity on weight trajectory. Results: Mean %BMIp95 was 129% (SD 24%), corresponding to severe obesity. Thirty percent of patients were food-insecure at baseline. After adjusting for other factors, monthly change in %BMIp95 was significantly smaller for food-insecure children compared to food-secure peers (difference in the coefficients for slope: 0.13, SE 0.05, p = 0.009). The modeled 12-month change in %BMIp95 was significant for food-secure children (-2.28, SE 0.76, p = 0.0026), but not for food-insecure children (-1.54, SE 1.22, p = 0.21). Conclusion: Household food insecurity was associated with a less optimal weight trajectory among children with obesity.