Radiation synovectomy (RS) has been used to treat chronically inflamed joints refractory to treatment using conventional agents. In RS, the radioactive isotope is concentrated in the synovial membrane from the injected colloid suspension, where it exerts its activity. However, despite numerous reports confirming its safety and efficacy, this procedure is not widely practised. In the Singleton Hospital NHS Trust, yttrium(90) (Y(90)) RS has been practised since 1990 for refractory synovitis. In this study, we analyse the results of therapy and complications in 38 joints so treated. Doses of 10 mCi were used in the majority of patients. Most responses were apparent by 6 months following the procedure. Altogether, 68% of the treated joints showed satisfactory response at 3 years, with 29% having all symptoms under control beyond 3 years. In three patients, there was evidence of minor pigmentation at the injection site. Two patients had extravasation of the isotope and needle track ulcers, which were recorded as major toxicity. We find Y(90) radiosynovectomy to be safe, quick, and effective in the management of patients with refractory synovitis. The efficacy of RS should be tested in randomised clinical trials involving large numbers of patients.