Background The Haemo-QoL project aims at developing and testing a quality of life assessment instrument for children and adolescents with haemophilia. It started in 1998, as scientific co-operation of a several European Haemophilia Care Centers upon recognition of the fact, at that time, no instrument to assess quality of life in the paediatric haemophilia population was available. Accordingly, the aim of the project was to develop and test such a measure for use in Europe. The project, funded by Bayer Biological Products, was conducted according to a four-step procedure, which was outlined in an accompanying study protocol. The 4 steps concerned The development of relevant quality of life questions (items) and their translation The pilot testing of the questionnaire with appropriate modification The field testing of the questionnaire The final statistical analysis and report The project has ended in 2002 and has resulted in 3 sets of psychometrically tested questionnaire versions for three age groups of children as well as their parents, available in 21 languages, which are now ready for use in clinical and epidemiologcial trials. In addition to the full version, a short version for small children (4-7 years) containing 16 items and a short version for older children (8-16 years) containing 35 items were developed. An 8-item index version was developed spanning all age groups which is also available as a self and parent-report (Haemo-QoL-Index).