This paper discusses the behavioral evaluation of patients who seek bariatric surgery and the psychosocial complications most frequently observed in these individuals. The effects of such complications on surgical outcome are briefly examined, as is the challenge of predicting therapeutic response on the basis of preoperative variables. The paper concludes with a description of the goals and methods of a behavioral assessment used at the University of Pennsylvania. This evaluation includes the use of the Weight and Lifestyle Inventory, a questionnaire that guides our interview with patients.