This was a multicenter, open-label, randomized (patients are assigned different treatments based on chance), dose-titration, parallel-group study characterizing the effectiveness and safety of OROS hydromorphone HCL and OxyContin in adult patients with osteoarthritis (OA) of the knee or hip who were unable to consistently control or treat their osteoarthritis pain with non opioid medications or with as-needed use of an opioid analgesic. The study consisted of a 14-day period for randomization, dose-titration, and stabilization, followed by a 4-week maintenance phase. Eligible patients were randomized equally to begin therapy with either OROS hydromorphone HCL 8 mg daily or OxyContin 10 mg twice daily. Upward dose titration (doses with increase in titration) from the starting doses was allowed every 2 days, based on pain relief and opioid-related side effects. The dose was to have been titrated to provide the best balance between pain relief and side effects. After 14 days, if therapeutic efficacy with dose stabilization had been documented, the patient was allowed to begin the 4-week maintenance phase. The expected primary efficacy variable endpoints were: The mean pain relief score at endpoint defined as the mean of the last 2 non missing pain relief scores during the Maintenance Phase, and the days from study medication initiation to the third day of moderate to complete pain relief on the patient's final titrated dose (as reported in the patient diary) during the Randomization, Titration and Stabilization Phase. Safety was evaluated by adverse events (AEs), vital signs, and physical examinations. OROS hydromorphone HCL 8mg tablet orally daily or OxyContin 10mg tablet orally daily; Upward dose titration from the starting doses was allowed every 2 days, based on pain relief and opioid-related side effects; After 14 days of efficacy with dose stabilization, patient was allowed to begin the 4 week maintenance phase.