Fragile Families and Wellbeing Study (FFS) data were analyzed to examine the relationships between obesity, household instability, and area poverty in urban mothers and their children (N = 1,449). The FFS was conducted in 20 U.S. cities between 2001 and 2004. Household instability was defined as a tenuous home environment where certain psychosocial and economic constraints are present. Area poverty was determined according to the 2000 U.S. Census. Relative weight increased with level of household instability in mothers but not in children. Mothers with the highest level of household instability within areas of low poverty (i.e., relatively little poverty) were more likely than others to be obese (Odds Ratio = 1.8, 95% CI 1.2–2.6). Household instability was not associated with overweight in children. These results suggest that home stability should be considered as a possible risk factor for obesity in mothers with infant children, particularly those residing in low poverty areas.