248 patients with symptomatic knee osteoarthritis were randomized to one of three treatment groups: topical diclofenac sodium gel, a vehicle-control group that administered only the carrier solution, and a placebo group. Patients were to apply the allocated interventions for 4 weeks. Patients were assessed for outcome on the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), a Patient Global Assessment, and the Incidence of adverse events. After 4 weeks, reduction in each of the WOMAC Pain, Physical Function, and Stiffness subscales was significantly greater in the topical diclofenac group compared to both the vehicle-control group and the placebo group.