Introduction: Early initiation of prophylaxis in severe haemophilia is critical for effective prevention of arthropathy. However, the optimum time for starting prophylaxis has not been established yet. Aim: This study assessed long-term effects of age at starting prophylaxis and joint bleeding before prophylaxis on haemophilic arthropathy. Methods: In patients with severe haemophilia (FVIII/IX −1), born between 1965 and 2000, haemophilic arthropathy was evaluated on X-rays. Patient groups were compared by multivariable regression analysis, adjusted for bleeding phenotype and lifetime intensity of prophylaxis. Results: One hundred and twenty-four patients were evaluated at a median age of 22 years. When comparing patients according to age at starting prophylaxis, starting before age 6 years was significantly better than starting later (P