Weight loss surgery, particularly the Roux-en-Y gastric bypass (REYGB), has become a popular treatment strategy for obesity. Often the only measure of success is the amount of weight lost following surgery. Unfortunately the nutritional adequacy of the postoperative diet has frequently been overlooked, and in the months to years that follow, nutritional deficiencies have become apparent, including protein-calorie malnutrition and various vitamin and mineral deficiencies contributing to medical illnesses and limiting optimal health. Therefore, patients require close monitoring following REYGB, with special regard to the rapidity of weight loss and vigilant screening for signs and symptoms of subclinical and clinical nutritional deficiencies. Several specific nutrients require close surveillance postoperatively to prevent life-threatening complications related to deficient states. This article addresses nutritional concerns associated with REYGB with fastidious focus on recognition and treatment of the nutritional deficiencies and promotion of nutritional health following REYGB. Recommendations regarding nutritional intake following REYGB are based on available scientific data, albeit limited. In cases where data do not exist, expert or consensus opinion is provided and recommendations for future research are given. Ultimately, clinical application of this information will contribute to the prevention of nutrition-related illness associated with REYGB.