OBJECTIVE - To examine associations of neighborhood characteristics with six components of the insulin resistance syndrome (IRS) in young adults. RESEARCH DESIGN AND METHODS - Cross-sectional data from the Coronary Artery Risk Development in Young Adults (CARDIA) Study were used to examine associations of neighborhood characteristics with the IRS in 3,093 nondiabetic adults aged 28-40 years. Measures of BMI, fasting HDL cholesterol, triglycerides, insulin, glucose, and systolic blood pressure were combined into an IRS score. U.S. Census-derived neighborhood characteristics were summarized into a neighborhood socioeconomic score, with an increasing score signifying increasing socioeconomic advantage. RESULTS - Among white men and women, the IRS score was inversely related to neighborhood socioeconomic score. Neighborhood characteristics remained associated with the IRS score after controlling for personal income and education (adjusted mean differences for 95th vs. 5th percentile of neighborhood score: -0.24 standard deviation units [SE = 0.12] in men and -0.56 standard deviation units [SE = 0.10] in women). Among black participants, neighborhood score was inversely associated with IRS score in persons of high income and education (mean differences 95th vs. 5th percentile -0.54 [SE 0.26] in men and -0.52 [SE 0.26] in women) but positively associated or not associated with IRS score in persons of low income and education (mean differences 0.60 [SE 0.21] in men and 0.00 [SE 0.16] in women). CONCLUSIONS - The IRS score is associated with neighborhood characteristics as early as young adulthood. Features of residential environments may be related to the development of insulin resistance.