We sought to determine whether the Edmonton Obesity Staging System (EOSS), a newly proposed tool using obesity-related comorbidities, can help identify obese individuals who are at greater mortality risk. Data from the Aerobics Center Longitudinal Study (n = 29 533) were used to assess mortality risk in obese individuals by EOSS stage (follow-up (SD), 16.2 (7.5) years). The effect of weight history and lifestyle factors on EOSS classification was explored. Obese participants were categorized, using a modified EOSS definition, as stages 0 to 3, based on the severity of their risk profile and conditions (stage 0, no risk factors or comorbidities; stage 1, mild conditions; and stages 2 and 3, moderate to severe conditions). Compared with normal-weight individuals, obese individuals in stage 2 or 3 had a greater risk of all-cause mortality (stage 2 hazards ratio (HR) (95% CI), 1.6 (1.3-2.0); stage 3 HR, 1.7 (1.4-2.0)) and cardiovascular-related mortality (stage 2 HR, 2.1 (1.6-2.8); stage 3 HR. 2.1 (1.6-2.8)). Stage 0/1 was not associated with higher mortality risk. Lower self-ascribed preferred weight, weight at age 21, cardiorespiratory fitness, reported dieting, and fruit and vegetable intake were each associated with an elevated risk for stage 2 or 3. Thus, EOSS offers clinicians a useful approach to identify obese individuals at elevated risk of mortality who may benefit from more attention to weight management. Further research is necessary to determine what EOSS factors are most predictive of mortality risk, and whether these findings can be generalized to other obese populations.