The purpose of this study was to examine the conceptual gap between self-perceived weight and body mass index (BMI), and to assess the knowledge gap between perceived importance of following dietary guidelines and health literacy levels. Adults (n = 131) eligible for the Supplemental Nutrition Assistance Program (SNAP) were interviewed at eleven SNAP regional offices in Maryland. Based on BMI calculated from self-reported height and weight, 65.6% of participants were overweight or obese while 40.5% perceived that they were overweight or obese. In sub-group analysis categorized by BMI, only 20.0% in the overweight and 20.0% in the obese group correctly perceived themselves as being overweight or obese. Following dietary guidelines was perceived as important by a majority of participants, but only 43.5% had adequate health literacy. Conceptual and knowledge gaps between self-perception and objective health status existed in the low-income SNAP-eligible sample. Future studies need to address these gaps because misperceived weight status and insufficient health literacy are critical barriers to inducing behavioral change.