The Obesity Society (TOS) commissioned a panel of experts from among its members to undertake a review of the issue of labeling obesity a disease and to examine pertinent evidence and arguments. The panel unanimously and strongly stated that obesity is a complex condition with many causal contributors, including many factors that are largely beyond individuals' control; that obesity causes much suffering; that obesity causally contributes to ill health, functional impairment, reduced quality of life, serious disease, and greater mortality; that successful treatment, although difficult to achieve, produces many benefits; that obese persons are subject to enormous societal stigma and discrimination; and that obese persons deserve better. Whether obesity should be declared a disease is controversial, and thoughtful arguments have been made on both sides of the issue. The panel recognized that there is a clear majority view among the general public as well as among authoritative bodies that it is reasonable to call obesity a disease. The panel reviewed three broad classes of argument as to whether obesity is rightly classified as a disease. The first, the scientific approach, proceeds in two conceptually simple steps: i) identify the characteristics that entities must have to be considered diseases and ii) examine empirical evidence to determine whether obesity possesses those characteristics. The scientific approach would be well suited to answering the question "is obesity a disease?" rather than "should we consider obesity a disease?," were the former question answerable. However, after much deliberation, the panel concluded that the former question is ill posed and does not admit an answer. This is not because of a lack of agreement or understanding about obesity but rather because of a lack of a clear, specific, widely accepted, and scientifically applicable definition of "disease" that allows one to objectively and empirically determine whether specific conditions are diseases. The second type of argument, the forensic approach, entailed looking to the public statements of authoritative bodies as evidence of whether obesity is a disease or should be considered a disease. A nearly exhaustive search for and consideration of the statements made by ostensibly authoritative bodies made apparent that there is a clear and strong majority leaning - although not complete consensus - toward obesity being a disease. However, although some authoritative bodies have offered statements that obesity is (or is not) a disease, very few of them have published a thorough and rigorous argument or evidential basis in support of the statement. Moreover, and far more importantly, the panel held that the opinions of authoritative bodies tell us - at most - what is lawful, consistent with mainstream opinions, or likely to be supported by others. Such opinions are insufficient to tell us what is true or what is right. The panel strongly endorsed the position that there can be no higher authority than reason. Hence, the forensic approach was judged to be inadequate to help us determine either whether obesity is a disease or whether it should be considered a disease. The third approach to this question we termed the utilitarian approach. Recognizing that there is no clear agreed-on definition of disease with precise, assessable criteria that can be articulated, it seems that conditions that produce adverse health outcomes come to be considered diseases as the result of a social process when it is assessed to be beneficial to the greater good that they be so judged. Such judgments about likely benefit to the greater good are utilitarian judgments that may take empirical input but must also assume certain values. We considered the likely outcomes of considering obesity to be a disease to address the question "should obesity be declared a disease?" (as opposed to "is obesity a disease?"). Necessarily, our utilitarian analysis was speculative. The disease label tends to confer certain benefits, obligations, motivations, and legal considerations in our society. The panel concluded that considering obesity a disease is likely to have far more positive than negative consequences and to benefit the greater good by soliciting more resources into prevention, treatment, and research of obesity; encouraging more high-quality caring professionals to view treating the obese patient as a vocation worthy of effort and respect; and reducing the stigma and discrimination heaped on many obese persons. The panel felt that this utilitarian analysis was a legitimate approach to addressing the topic, as well as the approach used for many other conditions labeled diseases, even if not explicitly so. Thus, although one cannot scientifically prove either that obesity is a disease or that it is not a disease, a utilitarian approach supports the position that obesity should be declared a disease.