In 1997 the European Commission published Radiation Protection 91: 'Criteria for acceptability of radiological (including radiotherapy) and nuclear medicine installations'. This document specified the minimum criteria for acceptability. It has been used to this effect in legislation, codes of practice and by individual professionals. In a single document, it defined a level of performance at which remedial action was required. The document specified a series of parameters which characterised equipment performance and acceptable levels of performance. In its time it proved to be a useful document which was applied in member states to various degrees. Since the publication of Report 91 in 1997(1), a series of weaknesses emerged over time. Development of new radiological systems and technologies, as well as improvements in traditional technologies, has created circumstances where the acceptability criteria were in need of review. These weaknesses were recognised by the European Commission and a tender for its revision was issued. The criteria were developed by a team drawn from a broad range of backgrounds including hospitals, industry, government bodies, regulators and standardisation organisations. Representatives were mainly from Europe, but individuals from the American Association of Physicists in Medicine and International Atomic Energy Agency were included in the drafting process. This study describes the process employed in developing the revised document and the consultation process involved. One of the major difficulties the revision team encountered was related to an understanding of the actual meaning of the EC Directive. The view taken by the revision team was that Article 8, paragraph 3 places responsibilities on both the holders of radiological equipment and competent authorities. The acceptability criteria have been produced consistent with the European Commission's Medical Exposures Directive, which requires that patient exposures are optimised and justified.