92 patients with Kellgren-Lawrence grade III knee osteoarthritis were randomized to three weekly intraarticular injections of either low molecular weight hyaluronic acid (LMW HA; Orthovisc, Anika Therapeutics) or high molecular weight hyaluronic acid (HMW HA; Hylan G-F20, Synvisc, Wyeth). Patients were assessed for improvement from baseline in pain at rest, pain during activity, pain during stair climbing, pain during transfer activities, walking distance, knee range of motion, and Hospital for Special Surgery (HSS) score after 1, 2, 3, and 6 weeks, and 3, 6, and 12 months. Significant differences in improvement in pain were noted in favour of the LMW HA group for pain at rest at 3 months and pain during activity at 6 weeks. Nonetheless, all measures demonstrated non-significant differences between groups at 6 and 12 months.