摘要The annex A of the United Nations Scientific Committee on the Effects of Atomic Radiation(UNSCEAR)2020/2021 Report presented a comprehensive global estimate of frequencies and doses from medical exposure to ionizing radiation,their distribution and trends for the period 2009-2018.The annex considered four general categories of medical practice using ionizing radiation:(a)diagnostic radiology,including dental radiology and computed tomography,(b)interventional radiology(image-guided interventional procedures),(c)nuclear medicine,and(d)radiation therapy.In the period 2009-2018,about 4.2 billion medical radiological examina-tions were performed annually,resulting in an annual effective dose of 0.57 mSv per caput.The use of computed tomography has continued to grow and the contribution from interventional radiology has increased rapidly in recent years.The annual number of radionuclide therapy treatments has increased by 60％since the UNSCEAR 2008 Report,while the number of courses of radiation therapy has increased by 22％.Medical exposure remains by far the largest human-made source of radiation exposure to the public.The Committee's evaluation relies on the collection of up-to-date and representative exposure data from all Member States of the United Nations.Future exposure survey should be more relevant and useful and adapted to changing data sources and changing uses of radiation across the world.