There are significant economic and psychological costs associated with the negative weight-based social stigma that exists in American society. This pervasive anti-fat bias has been strongly internalized among the overweight/obese. While the etiology of weight stigma is complex, research suggests that it is often greater among individuals who embrace certain etiological views of obesity or ideological views of the world. This investigation examined 1) the level of internalized weight stigma among overweight/obese treatment seeking adults, and 2) the association between internalized weight stigma and perceived weight controllability and ideological beliefs about the world ('just world beliefs', Protestant work ethic). Forty-six overweight or obese adults (BMI >or=27 kg/m2) participating in an 18- week behavioral weight loss program completed implicit (Implicit Associations Test) and explicit (Obese Person's Trait Survey) measures of weight stigma. Participants also completed two measures of ideological beliefs about the world ("Just World Beliefs", Protestant Ethic Scale) and one measure of beliefs about weight controllability (Beliefs about Obese Persons). Significant implicit and explicit weight bias was observed. Greater weight stigma was consistently associated with greater endorsement of just world beliefs, Protestant ethic beliefs and beliefs about weight controllability. Results suggest that the overweight/obese treatment seeking adults have internalized the negative weight-based social stigma that exists in American society. Internalized weight stigma may be greater among those holding specific etiological and ideological beliefs about weight and the world.