Using differential item functioning (DIF) analyses, this study examined whether there were any DIF items in the National Health and Nutrition Examination Survey (NHANES) physical activity (PA) questionnaire. A subset of adult data from the 2003-04 NHANES study (n = 3,083) was used. PA items related to respondents' occupational, transportation, domestic, leisure-time, strength-related, and sedentary activities were analyzed for DIF using Mantel-Haenszel, SIBTEST, and analysis of variance procedures. Some items were identified as DIF items, with the majority of those items favoring advantaged social groups. For example, items about domestic activity and moderate-intensity leisure-time activity were DIF items favoring non-Hispanic Whites, and persons with higher levels of education (e.g., some college or more) or income (e.g., annual family income [AFI] greater than $34,999). The vigorous activity item was a DIF item favoring younger adults (ages 20-59 years) and persons with higher levels of education or income. Occupational PA presented DIF favoring Hispanics and persons with lower levels of education (e.g., high school or less), and the transportation-related PA item presented DIF favoring persons with lower incomes (e.g., AFI [less than or equal to] $34,999). These findings highlight the importance of conducting DIF analysis in PA survey construction and emphasize the need to introduce DIF concepts and methods to PA researchers. (Contains 4 tables.)