Objectives. We investigated the association between housing insecurity and the health of very young children. Methods. Between 1998 and 2007, we interviewed 22 069 low-income caregivers with children younger than 3 years who were seen in 7 US urban medical centers. We assessed food insecurity, child health status, developmental risk, weight, and housing insecurity for each child's household. Our indicators for housing insecurity were crowding (qqqgt; 2 people/bedroom or qqqgt; 1 family/residence) and multiple moves ( 2 moves within the previous year). Results. After adjusting for covariates, crowding was associated with household food insecurity compared with the securely housed (adjusted odds ratio [AOR] = 1.30; 95% confidence interval [CI] = 1.18, 1.43), as were multiple moves (AOR = 1.91; 95% CI = 1.59, 2.28). Crowding was also associated with child food insecurity (AOR = 1.47; 95% CI = 1.34, 1.63), and so were multiple moves (AOR = 2.56; 95% CI = 2.13, 3.08). Multiple moves were associated with fair or poor child health (AOR = 1.48; 95% CI = 1.25, 1.76), developmental risk (AOR 1.71; 95% CI = 1.33, 2.21), and lower weight-for-age z scores (–0.082 vs –0.013; P = .02). Conclusions. Housing insecurity is associated with poor health, lower weight, and developmental risk among young children. Policies that decrease housing insecurity can promote the health of young children and should be a priority.