This study was a short-term, non-randomized (each patient was assigned the same treatment from phase I through phase III by the researchers), non-comparative, open-label, repeated dose study of OROS® hydromorphone HCL consisting of 3 phases: Phase 1 - prior opioid stabilization phase (2-7 days); Phase 2 - OROS® hydromorphone HCL conversion, titration, and stabilization phase (3 - 14 days); Phase 3 - OROS® hydromorphone HCL maintenance therapy phase (28 days) Before Phase 1, patients must have had no change in their prescribed opioid regimen over the prior 30 days. During Phase 1, patients were to have demonstrated 2 consecutive days of stable baseline oral or transdermal opioid medication.