Out of the almost 20,000 particle accelerators in operation worldwide, about half of them are used in the medical field. The lecture will review the two major applications in this domain: radionuclide production and cancer radiation therapy with electron, photons and hadron beams. The pros and cons of reactor versus cyclotron production of medical radionuclides will be illustrated, along with the possibility of accelerator production (using either electrons or protons) of the radionuclide most widely used in medical imaging, the 99Mo/99mTc generator, presently made at nuclear reactors. Cancer radiation therapy largely relies on electron linacs operating in the energy range 6-25 MeV: some of the most advanced treatment modalities of these "conventional" devices will be described. The state-of the-art is represented by radiation therapy with protons and carbon ions, which require cyclotrons or synchrotrons with energy up to 250 MeV and 400 MeV/u, respectively, and complex transport and irradiation systems. The lecture will close with a hint to future accelerator developments in this domain.