Osteoarthritis is a chronic disease that causes serious pain and limitations in activities. Intraarticular corticosteroid injections combined with pharmacological treatment and physiotherapy have been used for years to control the local inflammation and relieve pain in the patients with osteoarthritis. There are several animal experiments which suggested that the intraarticular corticosteroid injections impair cartilage protein synthesis. However, there are no serious evidences suggesting the increase of cartilage impairment. The aim of our study was to compare the efficacy of placebo and intraarticular corticosteroid agents in the patients with symptomatic knee osteoarthritis. One hundred and twenty patients with painful knee osteoarthritis were included in the prospective, randomized, controlled study. The patients were randomized into four groups. Each group consisted of thirty patients. Intraarticular single dose of methylprednisolone acetate (40 mg, 1 ml), Betametazone disodium phosphate (3 mg, 1 ml), Triamsinolon acetonate (40 mg, 1 ml), and serum physiological (0.09% NaCl, 1 ml) were administrated to the groups, respectively. The patients were evaluated by Visual Analog Scale (0-10 cm [VAS]) for the pain severity, and by Lequesne Functional Index for functional state before treatment, and at the 1st, 3rd, 6th, and 12th weeks. Our results showed that single doses of three agents provided symptomatic and functional relief and their effects reduced at the 12th week. However, methylprednisolone acetate was a statistically more effective analgesic as compared to the other agents until the sixth week.