Purpose: To investigate response rates and predictors of treatment success in patients treated with total hip arthroplasty (THA). Methods: A prospective register-based cohort study including all consecutive primary THAs was conducted between 01/2006-12/2011. Primary outcomes were changes in WOMAC, according to OMERACT-OARSI, and minimal important difference (MID) in quality of life (EQ-5D) between baseline and 6-month follow-up. Socioeconomic and clinical predictors on treatment success were analysed by bivariate/multivariate regression. Results: The study population included 2,553 patients (mean age 60.8 years; 52.8% female) and 2,391 (93.7%) at follow-up. 2,194 (93.8%) (OMERACT-OARSI) and 2,131 (83.5%) (EQ-5D MID) patients were classified as responders. Predictors for treatment success vs treatment failure were not identified. Obese patients and patients living alone showed less pronounced, and patients with higher educational level more pronounced, improvements in the WOMAC at follow-up. Conclusions: Treatment with THA leads to improvement in function, decline in pain and increase in quality of life in the vast majority of patients.