Both household food insecurity and childhood overweight are serious public health problems that appear to be paradoxically correlated. This study examines the relationship between overweight and household food insecurity with/without hunger in low-income children participating in the Special Supplemental Nutrition Program for Women, Infants, and Children. Weight, height, and household food insecurity data were collected on 8,493 children ages 1 month to 5 years and analyzed by sex and age groups using logistic regression to model the odds of being overweight (weight for length or body mass index [calculated as kg/m(2)] for age > or =95th percentile) given household food insecurity status, controlling for race/ethnicity and maternal education. Analyses were stratified by age and sex because interaction terms with household food insecurity were significant (P<0.10). In this sample, prevalence of household food insecurity was 30.7% (8.3% with hunger) and 18.4% were overweight. Among girls younger than 2 years of age, household food insecurity was associated with reduced odds of overweight compared with food-secure households (odds ratio=0.65; 95% confidence interval: 0.47 to 0.88); hunger status did not alter this association. Among 2- to 5-year-old girls, there was no overall significant association between household food insecurity and overweight; however, household food insecurity with hunger was positively associated with overweight compared with those from food-secure households (odds ratio=1.49; 95% confidence interval: 1.06 to 2.10). No association between household food insecurity and overweight was found among boys. These findings suggest an association between household food insecurity and overweight prevalence in this low-income population. However, sex and age appear to modify both the magnitude and direction of the association.