The U.S. Household Food Security Scale, developed with federal support for use in national surveys, is an effective research tool. This study uses these new measures to examine associations between food insecurity and health outcomes in young children. The purpose of this study was to determine whether household food insecurity is associated with adverse health outcomes in a sentinel population ages less than or equal to 36 mo. We conducted a multisite retrospective cohort study with cross-sectional surveys at urban medical centers in 5 states and Washington DC, August 1998-December 2001. Caregivers of 11,539 children ages less than or equal to 36 mo were interviewed at hospital clinics and emergency departments (ED) in central cities. Outcome measures included child's health status, hospitalization history, whether child was admitted to hospital on day of ED visit (for subsample interviewed in EDs), and a composite growth-risk variable. In this sample, 21.4% of households were food insecure (6.8% with hunger). In a logistic regression, after adjusting for confounders, food-insecure children had odds of "fair or poor" health nearly twice as great [adjusted odds ratio (AOR) = 1.90, 95% CI = 1.66-2.18], and odds of being hospitalized since birth almost a third larger (AOR = 1.31, 95% CI = 1.16-1.48) than food-secure children. A dose-response relation appeared between fair/poor health status and severity of food insecurity. Effect modification occurred between Food Stamps and food insecurity; Food Stamps attenuated (but did not eliminate) associations between food insecurity and fair/poor health. Food insecurity is associated with health problems for young, low-income children. Ensuring food security may reduce health problems, including the need for hospitalizations.