Racial and ethnic disparities in obesity persist despite a narrowing in obesity risk associated with socioeconomic status. The household environment has been shown to be important in understanding obesity-promoting behaviors in diverse populations. Our current study was designed to examine the relationship between household density and obesity in young Black and White adults aged 18-30 years from the Coronary Artery Risk Development in Young Adults (CARDIA) cohort. All sociodemographic and leisure-time physical activity (LTPA) information for this study was collected by questionnaire between 1990-1991. Height was collected using a mounted centimeter ruler. Weight was measured on a balance beam scale. Obesity was defined as a body mass index > or = 30 kg/m2. Household density (HD) was defined as the ratio of people to bedrooms in the home. High HD was defined as a ratio > 1. Bivariate analysis showed that more women tend to live in high density households compared to men (45.4% vs 38.9%; P < .01) and more Blacks tend to live in high density households compared to Whites (53.7% vs 31.8%). Leisure-time physical activity index was lower in Blacks than in Whites (2.5% vs 2.6%; P < .01). Blacks had a higher prevalence of obesity than Whites (27.1% vs 11.8%; P < .01). Logistic regression analysis showed that Black women within high HD were at highest risk for obesity compared to White women living within low HD (OR = 4.88%; 95% CI: 3.56-6.67). HD may provide an important context in understanding racial disparities in obesity-promoting behaviors.