Cancer cachexia is a wasting syndrome that has been poorly characterized partly due to the lack of an adequate definition. In an attempt to establish diagnostic criteria, a formal consensus process was established, proposing three possible definitions for cancer cachexia: 1. Weight loss >5% over past 6 months (in absence of simple starvation); 2. Body mass index (BMI) <20 kg/m2 and any degree of weight loss >2%; 3. Sarcopenia (i.e. muscle depletion) defined by lumbar skeletal muscle index determined by computerized tomography (CT) imaging (men <55 cm2/m2; woman < 39 cm2/m2)and any degree of weight loss >2%. Using baseline data from a clinical trial (n=547 patients with lung cancer), we investigated the use of these different diagnostic criteria and hypothesized that each criterion would result in a similar prevalence of cachexia, consistently identifying individuals across definitions. Demographic characteristics including BMI and history of weight loss were used as well as CT images obtained as part of medical diagnosis. The prevalence of cachexia by each diagnostic criterion described above was approximately 47%, 8% and 41% for criterion 1, 2 and 3, respectively. According to McNemar test, cachexia diagnosis was not consistent among the three classifications: criterion 1 vs. 2, p = <0.0001; criterion 1 vs. 3, p = 0.021, and criterion 2 vs. 3, p =<0.0001. The recently proposed diagnostic criteria for cancer cachexia do not consistently identify individuals as having this condition, which may have potential unfavorable implications to research and clinical practice. ; Keywords: Cancer cachexia, Prevalence, Classification, Diagnosis, Computed Tomography, CT, Sarcopenia ; Submitted Note: A Thesis submitted to the Department of Nutrition, Food, and Exercise Sciences in partial fulfillment of the requirements for graduation with Honors in the Major. ; Degree Awarded: Spring Semester, 2014. ; Date of Defense: April 14, 2014.