To clarify the clinical benefits of administering immune-enhancing diet, Impact,we examined retrospectively the effect of preoperative immunonutrition with Impact on prevention of postoperative pneumonia after esophagectomy. In 47 patients without preoperative radiotherapy, no patient who preoperatively administered Impact>or=2,250 mL failed to develop pneumonia. The patients whose postoperative hospital stay was more than 30 days were administered Impact<or=2,000 mL except for one case. These results suggest that even preoperative administration of less amount of Impact than an estimated maximum dose, depending on patients' condition, may be beneficial to prevent postoperative pneumonia and a long hospital stay after surgery.