BACKGROUND: Numerous public health organizations have adopted national physical activity recommendations. Despite these recommendations, over half of the US population does not meet the minimum recommendation for physical activity, with large variations across individual US states. METHODS: Using the 2005 Behavioral Risk Factor Surveillance System (BRFSS) prevalence data for physical activity and obesity by state, we performed a weighted least squares regression using prevalence of obesity (BMI>or=30 kg/m2) as the dependent variable and insufficiently physically active (included completely sedentary), age, race, gender, and median household income as the independent variables. RESULTS: The unadjusted weighted least squares regression revealed a strong correlation between a state's prevalence of obesity and the prevalence of insufficiently physically active (R=.76, R2=.58, P<.0001). After adjusting for age, gender, race, and median household income, the prevalence of insufficiently physically active is still a significant predictor of the state prevalence of obesity (partial R=.44, R2=.19 P=.004). CONCLUSION: Macroenvironmental and sociopolitical disparities between individual US states that transcend simple state-level demographic factors need to be examined more rigorously to identify unique barriers and promoters of physical activity.