PURPOSE: Nutrition status is regarded as an important factor for postoperative morbidity in cancer surgery. The aim of this study was to evaluate the impact of the malnutrition risk, determined by Seoul National University Hospital-Nutrition Screening Index (SNUH-NSI), on operative morbidity after gastrectomy for gastric cancer. METHODS: This study enrolled 246 patients who had undergone gastrectomy for gastric cancer at Seoul National University Hospital from March 2009 to February 2010. We collected general patient information, SNUH-NSI at administration and related parameters (serum albumin, cholesterol, total lymphocyte counts, hemoglobin and body mass index), operative method, hospital stay and operative morbidity. RESULTS: The patients' mean age was 59.6+/-11.3 years, and 9.4% (n=23) of patients were rated as severe malnutrition risk. There was no difference in operative morbidity by age or sex. The patients with high risk of malnutrition by SNUH-NSI or with advanced gastric cancer showed higher operative morbidity (P<0.01). There were no relationships between biochemical parameters and operative morbidity. On multivariate analysis, the significant independent risk factors were severe malnutrition by SNUH-NSI (OR 2.627, 95% CI 1.033~6.679; P<0.05) and advanced gastric cancer (OR 2.023, 95% CI 1.074~3.811; P<0.05). CONCLUSION: Overall nutritional status, rather than single data, is more related to operative morbidity in gastrectomized patients. Especially severe malnutrition as determined by SNUH-NSI, is an independent risk factor for operative morbidity. Nutritional support to severely malnourished patient by SNUH-NSI is expected to be an effective approach in preventing complications after gastrectomy.