Obesity was recognized by the World Health Organization as a worldwide epidemic in 1998, and in no other nation is the trend toward increasing body weight more prevalent than the United States, where from 1990 to 2002 the median percentage of obese individuals increased from 11.6% to 22.1%. Since obesity is thought to be the result of a complex interaction of genetics, behavior, and the environment, an ecological perspective that considers individual-level factors in combination with various environmental and institutional-level influences can provide a comprehensive explanation for why obesity rates continue to increase. This study was designed to determine the influence of a select set of environmental and institutional variables on state-level obesity rates in the U.S. in 2000 and the increase in obesity rates from 2000 to 2005 after controlling for levels of physical inactivity. The percentage of state residents that did not participate in physical activity during the last month represented an individual-level indicator, while the average number of days hotter than 90º Fahrenheit and state per capita expenditures for the promotion of chronic disease control represented the environmental and institutional indicators respectively. The latter two variables were selected based on recommendations from previous applications of the ecological model to obesity. Data were collected from a variety of publicly accessible databases, and a series of six growth curve models were sequentially tested. Results indicated that after controlling for physical inactivity, the average obesity rate in 2000 was 18.06%, with an average increase of .08% per year. Subsequently, the average number of hot days per year predicted the initial obesity rate among states (γ 01= .021, p < .10), with a higher number of hot days resulting in higher rates of obesity. The average number of hot days did not predict the rate of change in the percentage of obesity; similarly, state budget expenditures for the promotion of chronic disease control did not predict either the initial rate or the rate of change in obesity. Taken together, the results suggest that while individual-level behaviors like physical inactivity are an important influence on obesity rates, environmental variables can also have a direct and indirect impact, perhaps by dictating individual-level behaviors like physical inactivity. Future studies should continue to assess the quality and impact of a more comprehensive set of individual and institutional influences on obesity, including eating behaviors. Keyword(s): disease prevention/wellness, exercise/fitness/physical activity, obesity issues