Background. Radiosynovectomy (radiosynoviorthesis) is an important instrument for the effective local treatment of chronic inflammatory joint disease, and provides an alternative to surgical synovectomy. Radiosynovectomy leads to the restoration of synovium in the treated joint, with improved joint function due to reduction of pain, swelling and stiffness. The radiopharmaceutical agent used in the treatment of the knee joint is yttrium90-citrate colloid. Material and methods. We studied 32 patients treated with 90Y -synovectomy of the knee between June and October 2004. 28 of these patients were suffering from rheumatoid arthritis, while 4 had chronic post-traumatic joint synovitis. All patients underwent 2-phase scintigraphy and ultrasound examination of the knee before and 6 months after the administration of 5 mCi 90Y-citrate. Results and Conclusions. Symptomatic relief and functional improvement of the treated knees were observed in 83% of the patients.