Population studies show that women have more pain and more obesity than men with aging. With the convergence of the obesity epidemic and the aging of the baby boomers, it is important to understand the impact of age and obesity on prevalence of pain. We studied the influence of age, gender and race/ethnicity on the association between obesity and chronic pain in the US population aged 25 and older using data from the National Health and Nutrition Examination Survey (NHANES)1999-2004. We calculated weighted prevalence by body mass index (BMI) according to age, sex and race/ethnicity groups, and performed multivariable logistic models using SUDAAN. We found that 33% of adults reported musculoskeletal pain lasting >1 month in the past year. Women had higher pain prevalence than men, and Whites greater than either Blacks or Mexican Americans. In women, obesity was associated with pain in all age groups, while in men this was only observed in middle age (45-64y). Among Whites, obesity was associated with pain in all age groups; in Blacks, the association was only observed in those aged 45 and older; in Mexican Americans, only in those younger than age 45. Substantial sex differences were observed in numbers of pain sites; 24% of obese(BMI>30) women had multisite pain compared to 15% of obese men. Prevalence of multisite pain was higher in obese Whites compared to obese Blacks and Mexican Americans. In multivariable models adjusted for sex and race/ethnicity, there was a significant interaction between age and BMI in the likelihood for chronic pain. These findings show that the relationship between obesity and chronic musculoskeletal pain varies according to age, sex and race/ethnicity. Further research is needed to understand underlying reasons for these differences.