The anatomic and physiological changes resulting from bariatric surgery can affect both nutrition and psychological attitudes. Modifications of the gastrointestinal tract lead to a diminished ability to absorb nutrients, electrolytes, and bile salts, as well as deficiencies in iron, calcium, and other vitamins and minerals. Dehydration, lactose intolerance, and protein calorie malnutrition are other common sequelae. Alterations in bone metabolism increase long-term risk for osteopenia and osteoporosis. Noncompliance with postsurgical nutritional regimens has been estimated to occur in from one third to almost two thirds of cases and can exacerbate these complications. Psychological issues are often present in patients with morbid obesity and can affect surgical outcomes. These issues include mood and personality disorders, destructive eating behaviors, and poor body image. Nearly one third of patients undergoing bariatric surgery also have a history of substance abuse disorder. The literature suggests that although the mental health of patients improves as a result of bariatric surgery, the benefits may be transient, and problems such as negative personality profiles, detrimental eating patterns, and negative body image persist to some extent. Identification of presurgical psychiatric problems can help identify those patients more likely to achieve lasting weight loss when surgery is combined with long-term follow-up to minimize medical and psychological complications.