Background and Aims: The aim of this study was to investigate the health-related quality of life before and after a hip and a knee arthroplasty operation using a 15D instrument and to compare these scores to the Finnish control population 15D scores. Materials and Methods: The pre- and post-operative data of 15D were prospective collected from the patients undergoing total hip arthroplasty or total knee arthroplasty at the Kuopio University Hospital. Post-operative data were collected at 6 and 12 months after the operation. Results: The mean change of the 15D score after hip arthroplasty was +0.062 and after knee arthroplasty, it was +0.033 at the 12-month follow-up ( p < 0.001). Total hip arthroplasty patients of all ages reached the control population 15D scores at the 12-month follow-up. Of the total knee arthroplasty patients, only patients aged >75 years and males aged 55–64 years did reach control population 15D scores at the 12-month follow-up. Patients experienced a statistically significant improvement in mobility, vision, sleeping, usual activities, discomfort and symptoms, distress, and vitality ( p < 0.05). Conclusion: Successful hip and knee arthroplasty operations improve patients’ health-related quality of life. According to this study, hip arthroplasty improves the health-related quality of life more than knee arthroplasty.