The topic of this thesis is a comparative analysis of the effects of physical activity and body mass indec on the indications of total hip and knee arthroplasty. On everyday basis more and more total joint arthroplasteis are being put in patients of every age. The reasons and causes are differents, however studies agree that there are clear correlations between decreased physical activity, increased body weight, the development of degenerative diseeases and finally in total joint arthroplasties (similarly in the cases of knee and of hip). Thus, the purpose of this research was to establish the effect of physical activity and body mass index on the indications of total hip and knee arthroplasty. The subjects in a trail were patients of the Clinic for Traumatology of KBC Sestre Milosrdnice (Sisters' of Mercy) situated in Zagrebu, who were questioned via questionnaire in June and July 2019. The trail composed of 53 individuals, with clear predominance of individuals with total hip arthroplasty. The information from the questionnaire were processed using the statistical methods (Hi kvadrat test and Mann-Whitney U test). The ratio of male/female subjects was equal, more than half were older than 65 years of age, and in most of the cases they were operated due to degenerative changes on their joints in the case of hip, while less than half was in the case of knee arthroplasty. The subjects, patients, they were not very physically active, only two of them were doing sports. In others, physical activity was measured exclusively in conducting everyday affairs by foot (walking). The numbers from the body mass index show that most of the patients are in the category of high body mass index. This research answered the hypothesis that decreased physical activity and high body mass index are contributing factor in total joint arthroplasty while simulthaneously point to the need of further research of this problematics.