It has become increasingly clear that one of the largest improvements in the outcome of cancer care could be obtained if all patients were selected to get the ‘state-ofthe-art’ treatment, at the correct time, and prescribed and administered in a correct form. This global process which should ensure the development of a cost-efficient medical practice is the prime interest of quality assurance (QA). While this would seem an obvious process to be integrated in the process of healthcare, it appears that relatively few organised initiatives have considered integrating the procedures to ensure quality assurance. The EORTC recognised earlier on the need to address and set up quality control procedures, first in the field of radiation oncology and later on in the other disciplines involved in cancer management. Several specific projects have been conducted between 1985 and 1996 covering, to a large extent, radiotherapy and medical oncology, as reported in the following papers. Although it was demonstrated that QA in surgery was possible and is actually addressed in individual protocols, various attempts at setting up a wide programme across diseaseoriented groups have not yet been successful. As a clinical research organisation, the EORTC has also investigated the impact of data quality and data transfer from the patient’s bed to the clinical trial database. All these programmes have substantially influenced the EORTC in developing specific procedures to monitor not only the quality of data, but also the quality of radiotherapy and in ensuring adequate prescription, preparation and reporting of chemotherapy administration. Many of these procedures are now inserted in all EORTC protocols. QA clearly remains a top priority at the EORTC, and it is through the activities of its Quality Assurance Committee, Quality Assurance Unit at the Data Center and Quality Assurance subcommittees of each Group that it is possible. Structural support (such as fellowships, for example) to the Groups that have specific projects in the field of QA in surgical oncology is now available. Furthermore, an increasing attention is paid to the field of pathology and diagnostic procedures for which the evolution of technology may now allow development of QA systems unthinkable a few years ago. This issue includes papers on: