Inactive lifestyles contribute to health problems and premature death and are influenced by the physical environment. The primary objective of this study was to quantify patterns of physical inactivity in New York City and the United States by combining data from surveys and accelerometers. We used Poisson regression models and self-reported survey data on physical activity and other demographic characteristics to predict accelerometer-measured inactivity in New York City and the United States among adults aged ≥18. National data came from the 2003-2004 and 2005-2006 National Health and Nutrition Examination Surveys. New York City data came from the 2010-2011 New York City Physical Activity and Transit survey. Self-reported survey data indicated no significant differences in inactivity between New York City and the United States, but accelerometer data showed that 53.1% of persons nationally, compared with 23.4% in New York City, were inactive ( P < .001). New Yorkers reported a median of 139 weekly minutes of transportation activity, compared with 0 minutes nationally. Nationally, 50.0% of self-reported activity minutes came from recreation activity, compared with 17.5% in New York City. Regression models indicated differences in the association between self-reported minutes of transportation and recreation and accelerometer-measured inactivity in the 2 settings. The prevalence of physical inactivity was higher nationally than in New York City. The largest difference was in walking behavior indicated by self-reported transportation activity. The study demonstrated the feasibility of combining accelerometer and survey measurement and that walkable environments promote an active lifestyle.