The European Organization for Research and Treatment of Cancer (EORTC) has taken a leading role in the development of the methodology of quality of life (QL) measurement. In the EORTC Quality of Life Study Group (QLSG) valid instruments to assess QL in a general manner and disease-specific modules have been developed to be used in oncological clinical trials. Statistical and methodological aspects of QL research are discussed. The application of QL assessments in clinical trials represents a subsequent challenge. To improve the practice of QL assessment in clinical trials an 'EORTC model' has been developed. This model requires the collaboration of liaison persons, the EORTC Cooperative Tumour Groups and the EORTC Data Centre Quality of Life Unit (QL Unit). Cooperation between these parties, protocol development and advantages and concerns of the model are mentioned in this paper. Finally, suggestions for improvement are proposed.