OBJECTIVE,The objective of the study was to evaluate the long-term impact of adjuvant chemoradiotherapy (CRT) on renal function through the creatinine clearance (Ccr) and renal parenchymal (RPR) volume and to compare the results with dose-volume histogram parameters in gastric cancer patients.,METHODS,This retrospective study was carried out from 2013 to 2014 in the Department of Radiation Oncology, Faculty of Medicine, Bulent Ecevit University, Zonguldak. Thirty-four patients who underwent post-operative CRT and were followed at least four years with Stage 1-3 gastric cancer were included in the study.,RESULTS,The median Ccr significantly decreased from 82.8 mL/min to 78.4 mL/min at 24 months and to 75.3 mL/min at 48 months after radiotherapy (RT) (p=0.034). Both RPR were significantly decreased 4 years after RT (p=0.001). Ccr reductions were >10 mL/min in 16 (47%) patients. The total kidney dose, bilateral kidney V20, bilateral kidney V25, and right kidney V20 doses were significantly higher in patients with decreased Ccr more than 10 mL/min at 48 months after RT than those who did not decrease (p=0.003, p=0.037, p=0.029, and p=0.013, respectively).,CONCLUSION,Long-term progressive renal toxicity with both functional and imaging tests was found after adjuvant CRT in gastric cancer. Decline in renal function was associated with bilateral and compensatory kidney radia-tion dose and volume. For RT planning, bilateral and compensatory kidney radiation dose and volume might be evaluated for safe dose constraints and may be useful for predicting late kidney toxicity.