Description A brief project description The Haemo-QoL project is co-ordinated by the study center at the University of Hamburg co-operating with researchers from six European countries. These countries are United Kingdom, the Netherlands, France, Germany, Spain and Italy. Children and adolescents with haemophilia in the age groups 4–7, 8–12 and 13–16 years as well as their parents were included in the study. Clinical data from parents perspective and medical documentation obtained by physicians were also assembled. Item development phase: Using relevant literature and expert groups, domains of quality of life in children were identified, preliminary items were formulated and translated into the project languages (English, French, German, Italian, Spanish and Dutch) Pilot testing phase: The items identified were assembled in questionnaires for children aged between 4 and 16 years and their parents. In a pilot testing, 58 families from six European countries were recruited from the project partners, answered the questions and provided information about their evaluation of the items (cognitive debriefing). After exploratory psychometric testing, also using the information from the cognitive debriefing, the questionnaires were modified and included in the field study. Here three age group versions were used: I= 4–7 years, II= 8–12 years; III= 13–16/18 years. Field study: A total of 339 children and adolescents from six European countries participated in the field study. Children and their parents filled in a package of questionnaires including the Haemo-QoL questionnaire together with other questionnaires such as generic quality of life measurements and questions concerning psychosocial determinants during their visit at one of the 20 participating treatment centres. Age groups II and III took with them a second questionnaire, to be filled in at home and sent back after 2 weeks (retest). In addition physicians collected medical data. Final analysis and report: The questionnaire for each of the age groups (child and parent versions) was psychometrically tested for reliability and validity. In addition the distribution of quality of life scores were examined, and socio-demographic, psychosocial and medical determinants of quality of life were inspected. Statistical analysis for each age group questionnaire resulted in acceptable psychometric properties of the full versions (children I: 21 Items, a=.85; children II: 64 Items, a=.90 and adolescents III: 77 Items, a=.92). In addition a short version of the questionnaires for age groups II and III including 35 Items was developed. The Haemo-QoL questionnaire can be downloaded after registration and a description of other used questionnaire is available. Links to other related projects can be found under links.