Very few studies have addressed the question of adherence of haemophiliacs to their treatment. The aim of our study was to compare their levels of adherence to therapy and also to provide recommendations. Professionals of an international research company performed individual interviews with 30 patients in each of six European countries (France, Germany, Italy, Spain, Sweden and UK) resulting in a total of 180 patients. Twenty-eight interviews with haemophilia physicians and specialist nurses were also undertaken. Overall adherence to treatment was high (80-87% in each country). There was a positive correlation between greater adherence and younger age, prophylactic treatment, time spent with a haemophilia treatment centre (HTC) and the quality of the relationship with the haematologist and nurse. The four leading reasons for not using the prescribed amount of clotting factor or skipping the administration interval were reduction, fluctuation or disappearance of symptoms, forgetfulness, lack of time for treatment and convenience. These reasons differed according to the country and the age of the patient. The main suggestions made by patients to improve adherence related to HTC, environment and factor concentrates. Patients considered also that internet and electronic patient diaries were likely to improve adherence. In this selected group of European haemophilia patients, adherence to treatment appears higher than for most patients with other chronic diseases. However, it remains important to be aware of the possibility of non-adherence given the serious implications, particularly when considering a differently selected group of patients.