Current treatment guidelines advocate opioids for arthritis when standard analgesics produce inadequate relief. Efficacy, adverse effects (AEs), dosing regimens, physician expertise and patient preference influence treatment selection. This study assessed transdermal fentanyl (TDF) as a treatment option for osteoarthritis (OA) patients. This prospective, Canadian open-label, 8-week trial assessed the efficacy and safety of TDF in patients with OA of hip or knee with moderate-to-severe target joint pain inadequately controlled using weak opioids. TDF was initiated at 25 mcg/h and titrated to optimal pain control. Rescue acetaminophen 500 mg was allowed (maximum 4 g/day). The main endpoint was improvement in pain control assessment rating (five rating categories); pain intensity (0-10 numerical scale), functionality (WOMAC-OA Index), health-related quality of life (SF-36 Health Survey) and global impression were also evaluated. Eighty-one patients (61% female, mean age 60 years) were enrolled; 62 were evaluable. All had failed on previous weak opioid therapy, primarily codeine or codeine combinations. At treatment end, 65% rated pain control as improved (Pain Control Assessment rating change >or=1 category; p<0.0001); mean change in pain intensity was a reduction of greater than 2 (p<0.0001); almost 50% were maintained on TDF 25 mcg/h with less than 1.3 g/day of rescue acetaminophen. At 1 month and end of treatment, changes in the SF-36 physical global scale and individual sub-scores for the pain index and role-physical scales were highly significant (p<0.0001). Improvement in functionality was noted at 1 month and at end of treatment with significant reductions in total WOMAC score, individual pain, stiffness and physical function sub-scores (p<0.0001). AEs causing discontinuation (n=32) included nausea, dizziness and vomiting. Most treatment-related AEs were mild to moderate in intensity. TDF improved pain control, functionality and health-related quality of life in these patients. The findings support current recommendations for use of opioids such as TDF as a treatment option for a sub-population of patients with OA pain.