PURPOSE: To evaluate the clinical usefulness of phosphorus-32 chromic phosphate synoviorthesis in patients with hemophilia, recurrent hemarthrosis, and synovitis. MATERIALS AND METHODS: Forty-four P-32 colloid synoviorthesis procedures were performed in 38 patients with these abnormalities. P-32 colloid was injected intramuscularly in a dose of 1.0 mCi (37.0 MBq) in adult knees and 0.5 mCi (18.5 MBq) in adult elbows. A thin-window Geiger-Muller counter was used to survey treated joints, lymph nodes, and liver in order to detect leakage from the joint. Follow-up extended to a maximum of 4 years after treatment. RESULTS: No evidence of clinically significant leakage was seen. Twenty-two of 28 treatments (78%) with longer than 6 months follow-up were associated with improvement in range of motion and frequency of hemorrhage. Of 15 treatments with longer than 2 years follow-up, 10 (67%) were associated with improvement in range of motion; 12 (80%), with improvement in frequency of hemorrhage; and 12 (80%), with improvement in quality-of-life activities. CONCLUSION: P-32 colloid synoviorthesis is a clinically useful outpatient procedure in patients with hemophilia, recurrent hemarthrosis, and synovitis in whom hemostatic therapy has failed.