Background: The modified frailty index (mFI) has been shown to predict mortality and morbidity after major operations. The aim of the present study was to assess the mFI as a preoperative predictor of shortterm postoperative complications and 30-day mortality in patients undergoing gastrectomy for non-bariatric diseases.Methods: The American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP) database was queried for patients who underwent total or partial gastrectomy from 2005 to 2011. A mFI was calculated based on 11 variables as previously described. The population divided into the following four categories based on the mFI score: the non-frail (mFI 0), the low frail (mFI 1), the intermediate frail (mFI 2) and frail (mFI ≥3). Thirty-day mortality and postoperative complications were evaluated.Results: Overall, 5,711 patients underwent a gastrectomy for non-bariatric diseases. Higher mFI score was associated with higher rates of mortality (from 1.2% in the non-frail group to 10.7% in frail group, P<0.001), overall morbidity (26.7% vs. 51.1%, P<0.001), postoperative Clavien IV complication (6% vs. 24.6%, P<0.001), serious complications (19.3% vs. 42.6%, P<0.001), sepsis-related complications (8.4% vs. 16.4%, P<0.001), cardiopulmonary complications (5% vs. 20.7%, P<0.001) and failure to rescue (5.7% vs. 21.8%, P<0.001).Conclusions: Higher mFI score in patients undergoing non-bariatric gastrectomy, is associated with a stepwise greater risk of postoperative morbidity and mortality. MFI Score can be easily calculated preoperatively, from the patient's history, and it can be used as an exceptionally useful criterion for treatment planning.