Morbid obesity is a significant problem in the Western world. Recently, there has been an increase in the number of patients undergoing surgical weight loss procedures. Currently, the most widely performed procedure is the Roux-en-Y gastric bypass operation which combines restriction of food intake with malabsorption of calories and various nutrients, resulting in weight loss and nutritional deficiencies, respectively. Various types of anemia may complicate Roux-en-Y and commonly include deficiencies of iron, folate, and vitamin B12. Iron deficiency is particularly common and may result from many mechanisms including poor intake, malabsorption, and mucosal bleeding from marginal ulceration. However, less appreciated etiologies of nutritional anemia include deficiencies of B-complex vitamins, ascorbic acid, and copper. Replacement of the missing or decreased constituent usually reverses the anemia. Since physicians of various medical and surgical specialties are often involved with the postoperative care of bariatric patients, a review of anemia in this patient population is warranted.