This clinical trial tests the pain relieving effectiveness of OROS hydromorphone, a once-daily formulation of a strong opioid against placebo in patients, who are suffering from pain due to osteoarthritis of the hip or the knee and who previously did not receive any strong opioids.The clinical trial tests the effect of the treatment on symptoms of pain, stiffness and physical function. The effect of the treatment on parameters on health related quality of life as well as quality of sleep will be measured.