Radiosynoviorthesis plays an important role in local treatment of rheumatoid arthritis. Depending on the size of the joint, radionuclides are used at different depths of penetration. Data from the literature and our own results with 396 treated joints indicate that in 2/3 of cases good therapeutic effects are achieved, e.g. the effect on the local inflammatory process is comparable with surgical synovectomy. This is in agreement with the results of our longterm follow-up of 141 joints after radiosynoviorthesis. As with surgical synovectomy, early synoviorthesis was most successful; however, longterm observations revealed a slight increase in local recurrences. These and primary non-responder cases show a good response to secondary injection of radionuclides. The effect of intraarticular injection of isotopes is possibly due to irradiative action on the inflamed cells, with subsequent fibrosis of the synovium. Side effects of radiosynoviorthesis are rare and generally avoidable. Since late complications cannot be excluded, careful consideration should be given to the indication for radiosynoviorthesis. Radiosynoviorthesis represents an alternative treatment to surgical synovectomy in patients over 40 years of age.