Background - The Prognostic Nutritional Index (PNI) score is based on the level of lymphocytes and albuminemia. The aim of this study was to validate the pre-operative PNI score for predicting post-operative mortality and morbidity of patients operated on for gastric cancer. Methods - This retrospective study collected data from patients operated on for a gastric cancer at the surgical unit B of Charles Nicolle's hospital in Tunis between January 1st, 2008 and December 31, 2012. The main outcome measure was post-operative death within 30 days. The secondary outcome was post-operative morbidity (within 30 days). We have performed a descriptive analysis, a univariate and multivariate analysis with logistic regression and a ROC curve analysis. Results - 14 women and 26 men were enrolled, with a sex ratio of 1,85. The mean age was 63 ± 15. Post-operative mortality and morbidity rate were respectively 18% and 28%. The ROC curve allowed us to validate the PNI for predicting post-operative mortality in gastric cancer with a threshold level of 38 with sensitivity 100% and specificity 64%. PNI was also validated for post-operative morbidity with a threshold level of 38 with sensitivity 82% and specificity 66%. Conclusion - PNI was validated for predicting post-operative mortality and post-operative morbidity in gastric cancer.