A cohort study was performed to assess adherence to early prophylactic therapy and its effects on outcome in 49 patients with severe haemophilia born 1970-1980. Median age at start of prophylaxis was 5.5 years. The majority (69%) of patients interrupted prophylactic treatment one or more times of their own accord (median total interruption 2.2 years). Patients who discontinued prophylaxis at any point tended to have more arthropathy as measured by the Pettersson scale (median 8 points versus 4 points). One-third of these patients interrupted prophylaxis for longer periods and had permanently stopped taking prophylaxis at a mean age of 20.1 years (mean +/- SD duration 4.1 +/- 4 years) and consequently experienced 5.4 +/- 3.4) joint bleeds per year. This subgroup could be identified by a predictive score based on age at start of prophylaxis, weekly dose of prophylaxis, and joint bleed frequency on prophylaxis. In conclusion, while on prophylaxis, more than two-thirds of patients with severe haemophilia try to discontinue treatment, resulting in slightly more arthropathy. One-third of these patients permanently discontinue prophylaxis in adulthood, while maintaining a low number of joint bleeds.