To date, no study has objectively measured physical activity levels among U.S. adults according to the 2008 Physical Activity Guidelines for Americans (PAGA). The purpose of this study was to assess self-reported and objectively measured physical activity among U.S. adults according to the PAGA. Using data from the NHANES 2005-2006, the PAGA were assessed using three physical activity calculations: moderate plus vigorous physical activity ≥150 minutes/week (MVPA); moderate plus two instances of vigorous physical activity ≥150 minutes/week (M2VPA); and time spent above 3 METs ≥500 MET-minutes/week (METPA). Self-reported physical activity included leisure, transportation, and household activities. Objective activity was measured using Actigraph accelerometers that were worn for 7 consecutive days. Analyses were conducted in 2009-2010. U.S. adults reported 324.5 ± 18.6 minutes/week (M ± SE) of moderate physical activity and 73.6 ± 3.9 minutes/week of vigorous physical activity, although accelerometry estimates were 45.1 ± 4.6 minutes/week of moderate physical activity and 18.6 ± 6.6 minutes/week of vigorous physical activity. The proportion of adults meeting the PAGA according to M2VPA was 62.0% for self-report and 9.6% for accelerometry. According to the NHANES 2005-2006, fewer than 10% of U.S. adults met the PAGA according to accelerometry. However, physical activity estimates vary substantially depending on whether self-reported or measured via accelerometer.