Physical activity is associated with a range of health benefits, and its absence can have harmful effects on health and well being, increasing the risk for coronary heart disease, diabetes, certain cancers, obesity, and hypertension. CDC and the American College of Sports Medicine recommend that adults engage in at least 30 minutes of moderate-intensity physical activity on most days, preferably all days, to have a beneficial effect on their health. Two Healthy People 2010 objectives (objectives 22-1 and 22-2) are to increase the proportion of adults who engage in regular moderate or vigorous activity to at least 50% and to decrease the proportion of adults who engage in no leisure-time physical activity to 20%. To examine differences from 2001 to 2003 in overall U.S. and state- and territory-specific prevalence estimates of 1) adult participation in the minimum recommended level of physical activity and 2) physical inactivity among adults during lifestyle activities, CDC analyzed data from the Behavioral Risk Factor Surveillance System (BRFSS) surveys for 2001 and 2003. The findings indicated that more than half of U.S. adults continue not to participate in physical activity at a level recommended as beneficial to health. Concerted public health efforts at federal, state, and local levels are needed to improve participation in physical activity.