The purpose of this study was to examine the association between socioeconomic status (SES) and leukocyte telomere length (LTL) – a marker of cell aging that has been linked to stressful life circumstances – in a nationally representative, socioeconomically and ethnically diverse sample of US adults aged 20–84. Using data from the National Health and Nutrition Examination Survey (NHANES), 1999–2002, we found that respondents who completed less than a high school education had significantly shorter telomeres than those who graduated from college. Income was not associated with LTL. African-Americans had significantly longer telomeres than whites, but there were no significant racial/ethnic differences in the association between education and telomere length. Finally, we found that the association between education and LTL was partially mediated by smoking and body mass index but not by drinking or sedentary behavior.