A cohort study was performed among 214 patients with severe haemophilia, born 1944-1994, to describe changes in treatment over the last 3 decades and its effects on clotting factor consumption and haemophilic arthropathy. Data on treatment strategy, clotting factor consumption, and outcome were collected for 3567 patient years (from 1972 to 1998), and 493 Pettersson scores were analysed. Median follow up was 17 years (range 6-27 years), and median age in 1998 was 27.6 years. Since 1965, replacement therapy, prophylaxis, and home treatment have been used and treatment intensified. Over the last 3 decades, annual clotting factor consumption increased by 260%, for both prophylactic and on-demand treatment. Annual clotting factor consumption kg-1 increased during childhood and appeared to stabilize in early adulthood for patients born 1965-79, who were treated with early replacement therapy or early prophylaxis. In contrast, clotting factor consumption increased continuously for patients born before 1965, who had had no access to replacement therapy during the early years of their life. The annual number of joint bleeds decreased over the years. Arthropathy as measured by the Pettersson score generally became apparent around the age of 15 years and was lowest in patients treated with primary prophylaxis. In conclusion, clotting factor consumption has increased and haemophilic arthropathy has decreased due to the intensification of treatment for severe haemophilia over the last 3 decades. Annual clotting factor consumption stabilizes in adulthood for patients who receive early intensive treatment.