This article presents the results of radiation synovectomy in children with juvenile idiopathic arthritis (JIA) who were treated in the Department of Paediatric Rheumatology of the Institute of Rheumatology in Warsaw in 2005–2010. The diagnosis of juvenile idiopathic arthritis was established according to the ILAR classification (Table I). In childhood, the most often type of JIA is oligoarthritis; not infrequently only one, usually a big joint, is involved. Often in the course of polyarticular or systemic onset of JIA, the inflammation in joints is reduced or suspended except for one or two joints in which the inflammation is still active. In these cases, beside the general treatment, local treatment plays an important role: intraarticular glucocorticoid injections, chemical synoviorthesis of knees, arthroscopic synovectomies, surgical treatment and radiosynovectomies. 20 children with JIA had radiosynovectomy performed, in 16 cases one joint was treated, in 4 cases – two joints. Totally 24 joints were treated: 20 knee joints, 3 ankle joints and 1 wrist. In 14 joints, one injection of radioactive isotope was performed, in 10 – radioisotope was injected twice, in one case – three times. In this therapy, yttrium ⁹⁰Y colloid or rhenium ¹⁸⁶Re colloid was administered. In 13 children a good clinical response was achieved and in 16 joints the improvement in ultrasound examination was determined (65%). Unsatisfactory results were observed in 7 patients for 8 joints (35%) (Table II). In one child (among 37 radiosynovectomies) an adverse effect was recorded: a skin ulceration after the injection of radioisotope to the ankle. The ulceration healed up after 3 weeks. In some clinical situations radiation synovectomy is a valuable method of therapy in children with juvenile idiopathic arthritis complementary to the general therapy.