The impact of hip (THA) and knee arthroplasty (TKA) on patients' health-related quality of life (HRQOL), physical ability and functioning was assessed in a two year follow-up study of 276 hip and 176 knee patients. The eligibility criteria were a diagnosis of primary arthrosis, a primary operation, and total joint arthroplasty. Patients were interviewed by questionnaire prior to the operation and 6, 12 and 24 months after the surgery. Subjective health outcomes were assessed with the Nottingham Health Profile and the 15D, a fifteen dimensional HRQOL measure. Patients' physical ability was assessed using measures of activities of daily living, and of physical mobility. Patient related outcome variations were analyzed by regression models. Major improvements were observed for pain, sleep and physical mobility. On average, in most of the quality of life dimensions the patients attained a similar quality of life as the comparable general population and only 4.7% of hip and 9.7% of knee patients had a worse HRQOL score at all three post-operative measurements than at baseline. Naturally, those with the poorest HRQOL pre-operatively gained most from the operation. High age did not lessen HRQOL gains from THA, but in TKA the oldest patients gained least in terms of 15D scores. Hip, but not knee patients with a long education tended to have greater improvements in quality of life and functional ability.