Nutritional deficiencies are already present in many morbidly obese patients before weight-loss surgery. Appropriate preoperative detection and correction is essential. The severity and pattern of deficiencies is dependent on the presence of preoperative uncorrected deficiency, the type of procedure performed varying with the degree of restriction or the length of bypassed small intestine, the modification of eating behavior, the development of complications, compliance with oral multivitamin and mineral supplementation, and compliance with follow-up. Rigorous control of fluids and electrolytes with establishment of adequate oral nutrition is important in the immediate postoperative period. Regular follow-up of the metabolic and nutritional status of the patient is essential, with life-long multivitamin and mineral supplementation.