Between 1987 and 1991 we performed Yttrium-90 (Y-90) silicate radionuclide synovectomies on 40 joints of 20 haemophiliac patients with haemophilic arthropathy. All were male, their mean age was 31 yr and 15 of the 20 (75%) were HIV antibody positive. The number of joint bleeds and amount of factor (VIII and IX) replacement given in the 6 months pre- and 6 and 12 months post-radionuclide synovectomy was compared. Y-90 silicate synovectomy was shown significantly to reduce both the number of joint bleeds (P < 0.001) and factor usage (P < 0.001) in the 6 months after the procedure, a result maintained up to 12 months. Depot methyl prednisolone was co-administered with Y-90 but thought unlikely to contribute to joint response beyond 6 months. The reduction of joint bleeds and factor usage was even more dramatic in the 6- to 12-month period post-synovectomy although this was not reflected by the P value (P < 0.001). The reduction of joint bleeds and factor consumption post-synovectomy was most obvious in elbow joints, although the other joints as a group showed a significant reduction. Patients who were HIV antibody positive showed considerable improvement up to 12 months post-treatment, both in reduction of joint bleeds and as a consequence factor consumption. This improvement was seen to a lesser extent in the smaller HIV-negative group.