Hypertrophy and inflammation of the synovium with various underlying pathologies - such as rheumatoid arthritis, osteoarthritis, haemophilia and spondyloarthropathy - can be treated successfully by radiosynoviorthesis (RSO). For medium-sized joints (shoulder, elbow, wrist, hip and ankle), the radionuclide of choice is rhenium-186. We review the evidence for the efficacy of this local, relatively non-invasive therapy and evaluate its benefits and risks. We conclude good evidence of rhenium-186 RSO in rheumatoid arthritis and haemophilic arthropathy. In the remaining pathologies, up to now, the therapeutic efficacy has not been confirmed by today's most stringent criteria for clinical studies. The available data support rhenium-186 RSO as a suitable second-line treatment for patients in whom other therapies (including locally injected corticoids) have failed, as long as proper attention is paid to correct administration - including post-treatment immobilization and the co-administration of corticoids.