Introduction: Among provided risk factors for endometrial cancer, following factors are mentioned: concomitant chronic diseases, especially diabetes, hypertension and obesity, but their influence on the treatment results is still not fully recognized. Objective: The aim of the study was the evaluation of the concomitant diseases influence on the conjugated treatment results in endometrial cancer. Material and method: The study covered 880 endometrial cancer patients, treated with adjuvant radiotherapy, between 1992 and 1998 at Maria Sklodowska-Curie Memorial Cancer Centre in Warsaw. All patients were treated with typical surgery – hysterectomy and adnexectomy. In the analysed group were patients in I, II and III clinical stage, according to FIGO. As the criterion of the treatment effectiveness was the overall survival and disease-free survival accepted. The multivariate Cox’s analysis was performed. The following factors were analysed: clinical stage of the disease, the histological type of the tumour, grading, the depth of stromal invasion, age and the performance status, body mass index (BMI), the period of the hormonal activity and the presence of concomitant diseases. Results: Patients with diabetes were 1.56 times at death risk (p=0.008), and 1.38 times at the disease recurrence risk (p=0.047), when compared to the control group. Conclusions: There has been confirmed, that among the concomitant diseases, only diabetes demonstrated statistical significance, affecting as well overall survival as disease-free survival.