Backgrounds Preoperative chemotherapy (PCT) and chemoradiotherapy (PCRT) showed promising results for gastric cancers. However, the influence of preoperative adverse events (AEs) on postoperative complications remains unknown. The aim of this study was to identify correlations between them. Methods Clinical data and laboratory findings were retrieved retrospectively for 115 patients who underwent gastrectomy after PCT or PCRT between 2010 and 2013. Preoperative AEs and postoperative complications were classified according to the Common Terminology Criteria for Adverse Events (CTCAE) and Clavien-Dindo (CD) grading systems, respectively. Correlations between CTCAE grades and CD grades were analyzed, and clinical data and laboratory findings were compared among three groups classified according to CD grades: CD0, CD1/2, and CD3/4. Results There were 61 (53.0 %) patients in the CD0 group, 44 (38.3 %) patients in the CD1/2 group, and 10 (8.7 %) patients in the CD3/4 group. The CTCAE grades did not correlate with the CD grades. Only estimated blood loss (P = 0.019) and transfusion rate (P < 0.001) differed among the three CD groups. Conclusion There are no correlations between pre- and post-operative adverse events in the terms of severity grades in patients with advanced or metastatic gastric cancer who underwent gastrectomy after PCT or PCRT. Meticulous intraoperative manipulations should be emphasized.