Aim: The aim of this study was to evaluate the efficacy of Y-90 and Re-186 radiosynovectomy in patients with hemophilic synovitis. Methods: Radiosynovectomy was performed in 32 joints of 20 patients with hemophilic synovitis by using Y-90 citrate colloid in the knee and Re-186 sulfide colloid in the elbow, shoulder, and ankle. The indication for radiosynovectomy was the continuous presence of intra-articular blood or effusion and three or more hemorrhages into the same joint within the last 6 months. Response to therapy was first assessed at the 4th month with blood-pool imaging. Patients were followed up by clinical evaluation based on assessments of joint-bleeding frequency, using range of motion measurements at 6-month intervals for an average of 1 year (range, 9-15 months). Results: A marked decrease (an 80%-100% decrease) in bleeding episodes was seen in 24 of 32 (75%) joints, a moderate decrease (51%-79% decrease) in 1 (9%) joint, and a mild decrease (30%-50%) in 3 (13%) joints. Frequency of intra-articular bleeding after treatment was unchanged in only 13% of the joints. The number of hemarthroses significantly decreased after therapy (p < 0.05). The mean bleeding frequency of the joints were 1.7 +/- 0.9 and 0.3 +/- 0.7 per month before and after therapy, respectively. The ratios of joints which had marked improvement after therapy were 86% in the ankle, 73% in the elbow, and 58% in the knee. There was no significant difference between percent joint range of motion limitations measured before and after therapy (p > 0.05). The correlation between therapeutic outcome (in terms of joint bleeding) and the difference of pre- and posttherapeutic blood-pool indices were significant (r = 0.594; p < 0.05), while the correlation between therapeutic outcome and pretherapeutic radiologic scale and pretherapeutic blood-pool indices were not significant (r = 0.095; p > 0.05; r = -0.089; p > 0.05, respectively). Conclusion: Radiosynovectomy is a simple but quite effective and efficient procedure in limiting the frequency of joint hemorrhage in patients with hemophilia. Blood-pool imaging may be an objective means for monitoring therapy response in these patients.