In this study we examine the association between household food insecurity and seasonally high heating and cooling costs. Logistic regression models, controlling for socioeconomic and demographic characteristics, were estimated using data on household food security and economic and demographic data from the 1995-2001 Current Population Survey Food Security Supplements and state-level data on heating and cooling degree days from the National Oceanic and Atmospheric Administration. Low-income households, especially those consisting entirely of elderly persons, experienced substantial seasonal differences in the incidence of very low food security (the more severe range of food insecurity) in areas with high winter heating costs and high summer cooling costs. In high-cooling states, the odds of very low food security for poor, elderly only households were 27% higher in the summer than in the winter. In high-heating states, the pattern was reversed for such households; the odds of very low food security were 43% lower in the summer. In light of recent sharp increases in home heating and cooling costs in many parts of the U.S., it is important to understand the extent to which households make tradeoffs between heating and cooling costs and other basic needs that affect their food security.