PREAMBLE: Postoperative radiochemotherapy after surgical procedure greatly enhances overall survival and locoregional control of the disease in patients with adenocarcinoma of the stomach in the stage IB to IIIC of the disease. The acute consequences of such treatment methods are well known and successfully controlled with supporting therapy, while the later consequences are relatively indistinct, especially damage to kidney function. ----- STUDY GOAL: We have tried to assess the resulting damage to kidney function according to various formulas used to calculate GFR and define the incidence, occurrence dynamics and the stages of the damage. We were interested in the quality of patients' lives, as well as whether there was any connection between the patient's quality of life and the stage of the damage to kidney function. ----- STUDY PARTICIPANTS AND METHODS: The research has been conceived as a prospective cohort clinical study. It was carried out at the Institute of Oncology in Ljubljana, Radiotherapy Division. The subjects were brought into the study in the period from November 2009 leading up to March 2013. In total 118 patients were involved in the study. The period of monitoring following the end of the oncology treatment amounted to 5 years and consisted of 7 control examinations. Standardized EORTC QLQ C 30 questionnaire assessing the quality of patients' lives had been filled in prior to the post-operative radiochemotherapy and later during 3 control examinations (after the first, third and fifth year). ----- RESULTS: The estimated GFR level at the final control five years after the end of the oncology treatment was statistically significantly lower in comparison to the values prior to the adjuvant treatment, regardless of the formula used to calculate it. Statistically, the lowest results were obtained by calculating the eGFR according to the CG formula, and the average value at the final control examination was 71.2 ml /min / 1.73 m2. At the last control examination, 33.4 % patients displayed eGFR value lower than 60 ml/min /1.73 m2 according to the CG formula, 20 % patients according to the CKD- EPI formula and 17.7 % according to the MDRD formula. The most sensitive dose-volume parameter that can point to developing damage to kidney function is V12 Gy for a bilateral kidney that in our study amounted to 54 %. Statistical analysis of standardized EORTC QLQ C 30 questionnaires showed a significant rise in the general health condition and quality of our patients' lives when compared to the previous control examination. The damage to kidney function is clinically irrelevant and therefore has no bearing on the quality of life. The analysis of survival rate showed that all the patients died due to the progress of the underlying disease and that the overall survival (OS) is equal to the disease-specific survival (DSS) and amounted to 60.7 % The disease-free survival (DFS) amounted to 60.3 %. Locoregional control (LRC) amounted to 81.6 %. ----- CONCLUSION: Following the post-operative treatment with capecitabine, damage to kidney function and chronic kidney disease develop. The influence of kidney damage on the quality of life has not been proven. It is vital that the damage is revealed in the early stages of the kidney disease because changes in the way of life and renoprotective drugs can inhibit the progress of the disease into later stages. Due to the progressive character of radiation nephropathy, it is necessary to continue the systematic monitoring of these patients. Standardized EORTC questionnaire QLQ C30 represents a simple and economical manner of screening potential damage to many physical and psychological functions that require further multidisciplinary treatment.