Because selenium is seldom added to formulations for enteral nutrition (EN), postoperative patients who are supported with EN are at risk for selenium deficiency. This report describes four cases of suspected selenium deficiency in long-term EN. Two patients underwent pancreaticoduodenectomy, one underwent total gastro-pancreatectomy, and one underwent esophageal resection and reconstruction with jejunal autotransplantation. They all developed malabsorption syndrome within 2 yr after operation. Enteral nutritional support with an elemental diet was provided continuously for 7-11 yr. Over the past 1-2 yr they experienced increasing bilateral muscular pain and weakness in the legs, gait disturbance, palpitation, and shortness of breath. Investigation for possible trace element deficiency revealed very low levels of selenium in the blood. After 10-20 d of supplementation with daily intravenous administration of selenious acid 0.16 mg/d (100 micrograms/d of selenium), their blood levels of selenium rose and their symptoms resolved. They were then continued on a maintenance regimen of oral sodium selenite 0.13 mg/d (60 micrograms/d of selenium).