Summary. There is a lack of publications concerning the use of primary prophylaxis in developing countries. The aim of this study was to evaluate the effectiveness of primary prophylaxis therapy in preventing the development of arthropathy in children with severe haemophilia A or B. From January 1999 to April 2009, a prospective study was carried out involving 39 patients with severe haemophilia A or B. These haemophilia A and haemophilia B patients received 20–40 UI kg−1 of factors VIII and IX, three and two times per week, respectively. The patients were followed up by a multidisciplinary team. The analysis was carried out in 23 patients who had been on prophylaxis therapy for at least 12 months. The orthopaedic evaluation was performed according to the recommendations of the Orthopedic Advisory Committee of the World Federation of Hemophilia, by evaluating pain and bleeding, and by conducting physical examination and radiological assessment (Pettersson’s Joint Score and magnetic resonance): 82.6% of patients who had used the factor regularly did not present any clinical or radiographic changes in the studied joints; 17.4% used the factor irregularly at the beginning of the treatment and of those, most patients presented mild changes in the joints; and 4.3% presented transient knee and ankle pain in spite of regular factor use. The preliminary results of primary prophylaxis confirm its effectiveness in preventing haemophilic arthropathy. Socioeconomic factors did not play a significant role.