Despite recent advances including new therapeutic options and availability of primary prophylaxis in haemophiliacs, haemophilic synovitis is still the major clinical problem in significant patient population worldwide. We retrospectively reviewed our 10-year experience with Y-90 radiosynovectomy to determine the outcome in the knee joints of patients with haemophilic synovitis. Between 2002 and 2012, 82 knee joints of 67 patients with haemophilic synovitis were treated with Y-90 radiosynovectomy. The mean age was 16.8 ± 7.8 years (range: 5–39 years). The mean follow-up period was 39.6 ± 25.6 months (range: 12–95 months). Failure of therapy represented re-bleeding after a radiosynovectomy was used as an end point in patient time to progression (TTP) analysis. The median TTP was calculated as 72.0 ± 3.6 months (95% CI 64.8–79.1 months) in Kaplan–Meier analysis. The 1, 3 and 5-year survival rates were 89%, 73% and 63% respectively. Longer TTP (hazard ratio for progression, 2.5; P = 0.00) was evident in patients who have greater reduction in bleeding frequency within 6 months after radiosynovectomy. We did not find a relationship between the TTP and the following variables: age, type and severity of haemophilia, the presence or absence of inhibitor, the radiological score, range of motion status of joints and the pretreatment bleeding frequency. We concluded that Y-90 radiosynovectomy in knee joint represents an important resource for the treatment of haemophilic synovitis, markedly reducing joint bleeding and long-term durability, irrespective of the radiographic stage and inhibitor status.