Purpose: The purpose of this study was to evaluate the reliability and validity of a global physical activity classification (GPAC) measure employed in the National Health and Nutrition Examination Survey (NHANES). Methods: For validity assessment (N = 6039), the NHANES GPAC was compared to NHANES accelerometry data. For reliability assessment (N = 94), a convenience sample completed a 1 week test-retest of the GPAC. Results: The association between total physical activity and GPAC ranged from 0.25 to 0.40, with the range for moderate to vigorous physical activity (MVPA) and GPAC being 0.17-0.39. In general, associations were stronger for total physical activity and GPAC compared to MVPA and GPAC. Similarly, associations were generally stronger for men, younger individuals, and Mexican Americans. In the reliability assessment, the intraclass correlation (ICC) ranged from 0.58 to 0.90, with the older participants having the lowest ICC (0.58). Conclusion: Findings of this study demonstrate suggestive evidence of both reliability and validity for the NHANES GPAC.