The Food Stamp Program and the Special Supplemental Nutrition Program for Women, Infants and Children (WIC) address poor nutrition among low-income adults, infants, and children in the United States. Higher rates of obesity among the populations these programs serve have led to concern that the programs may, ironically, contribute to the problem. To analyze the relationships between program participation and body weight, the study used cross-sectional data spanning the period 1976-2002. The authors compared participants with nonparticipants subdivided into three income categories: income-eligible for food and nutrition assistance, moderate income, and higher income. Results were most striking for adult women receiving food stamps. The most recent data showed that, in contrast to prior years, women food stamp participants had a Body Mass Index similar to that of income-eligible nonparticipating women and women with moderate incomes and were no more likely to be overweight or obese. For other sex and age groups, the associations between program participation and weight were inconsistent over time and varied by race and ethnicity. These variations illustrate the difficulty of using cross-sectional data to establish causal relationships between food and nutrition assistance program participation and weight status.