Obesity poses substantial costs both to the individual and society, mainly through its impact on health and labor productivity. Because obesity is more prevalent among the poor some have raised concerns that food assistance programs may encourage excess weight. This paper investigates whether the U.S. Food Stamp Program contributes to adult participants' weight as measured by body mass index (BMI). Results suggest that the typical female food stamp participant's BMI is indeed more than 1 unit higher than someone with the same socioeconomic characteristics who is not in the program. For the average American woman, who is 5 ft 4 in. (1.63 m) tall, this means an increase in weight of 5.8 pounds (2.6 kg). While this association does not prove that the Food Stamp Program causes weight gain, it does suggest that program changes to encourage the consumption of high-nutrient, low-calorie foods should be considered.