A multicentre Phase II clinical trial was recently undertaken to document the value of treatment with recombinant human granulocyte colony-stimulating factor (rG-CSF) in children with congenital agranulocytosis. To assess the impact of such therapy on health-related quality of life (HRQOL), we developed a questionnaire that was administered to the parents of study patients, twice prior to the initiation of treatment, and then monthly thereafter for six months. The questionnaire focused on several aspects of HRQOL that we thought were important in this patient population, including functional status, general health perceptions, activity limitation, disease symptoms, and discomfort associated with therapy. In this paper, we describe the questionnaire that we developed and the process by which it was translated into several languages. We also report on the impact of rG-CSF therapy on HRQOL. A total of 130 questionnaires were administered to the parents of 19 study patients between the ages of four and one-half months and 18 years in 11 study centres in four countries. Although our sample size is small, our findings suggest that treatment with rG-CSF may result in significant improvements in general health perceptions, limitations of daily activities, and symptoms of the disease.