Radiation synovectomy by intra-articular injection of beta-emitting radionuclides is a reliable and easy-to-perform therapy without harmful side effects for the treatment of inflammatory rheumatoid as well as degenerative joint diseases. The indication for radiation synovectomy is based on both clinical symptoms and on proven hyperperfusion, with active synovitis being seen on a pre-therapeutic three-phase bone scan. In this study, the clinical response after 6-18 months, evaluated by a standardized questionnaire, was compared with the reduction of synovitis seen on three-phase bone scintigraphy after treatment of 475 joints in 151 patients. The best clinical results were obtained in cases of true rheumatoid arthritis (73.4%), with less in other kinds of arthritis (48.8%) such as psoriatic or reactive arthritis. Because of the inflamed synovium being the main target tissue, clinical results in osteoarthritis with severe bone destruction are poorer (33.9%). However, synovitis can be markedly reduced (in approximately 70%), regardless of the underlying diagnosis, as shown by post-therapeutic three-phase bone scanning. Radiation synovectomy can be recommended in all kinds of arthritis. It should also be considered in cases of osteoarthritis as a last therapeutic option prior to joint replacement.