Background. The quality of life is very important and continuously medicine gives more weight to how one intervention can improve the quality of life of patients. Diabetes mellitus is a disease of modern lifestyle and is a chronic metabolic disease that affects the level of health and quality of life. Aim of this study is to investigate the quality of life of patients with diabetes and the factors affecting it. Material and methods. The questionnaire used consists of two parts. The first concerns demographic questions for the patient and the condition of diabetes mellitus and the second questionnaire on diabetes-related quality of life ADDQoL 19. The study included 140 patients and was conducted from October to March 2015 the hospital Carl Thiem Klinikum of Cottbus, Germany. The statistical analysis will be done with statistical software «Statistical Package for the Social Science (SPSS) for Windows» and level of statistical significance was set to p=0.05. Results. Statistical significant difference showed in the present quality of life (Overview I) by gender of patients with p=0.011. Based on the presence of complications of the disease there is a statistical significant difference in the average of responses for the 19 areas of life (AWI: Average Weight Impact) with p=0.033. The diabetes school also shows statistical significant difference in the AWI with p=0.018. Furthermore based on the type of diabetes and the treatment showed a statistical significant difference in quality of life (Overview I) for type 2 by treating with pills (Overview I: 1.117) than insulin treatment (Overview I: 0.471) with p=0.008. Conclusions. Educating patients appears to improve the quality of life of patients and the adoption of the Diabetes school should be followed by other countries. An important factor affecting the quality of life is the treatment followed and especially positive effect shows the use of treatment with pills which also support our results.