Nanotechnology — based on microscopic particles with distinctive properties related to their chemical structure, mobility, and capacity to absorb energy — is one of the hottest new areas of medicine. The possible applications are seemingly endless, from detecting cancer, inhibiting metastases, and modifying bone implants to improving non-invasive imaging, delivering drugs, and aiding in surgery. The ability of nanoparticles to penetrate deep within the brain suggests they may become a treatment for neurological disorders and their role in pediatric cancer is a promise of the future. Will nanotechnology disrupt medicine? How big can the potential of particles just one-billionth of a meter in size really be, and what are the risks of exploiting it?