AbstractMany methods of labeling liposomes with both diagnostic and therapeutic radionuclides have been developed since the initial discovery of liposomes 40 years ago. Diagnostic radiolabels can be used to track nanometer‐sized liposomes in the body in a quantitative fashion. This article reviews the basic methods of single photon emission computed tomography (SPECT) and positron emission tomography (PET) imaging and labeling of liposomes with single photon and dual photon positron emission radionuclides. Examples of the use of these diagnostic imaging agents will be shown. The ability to track the uptake of liposomes in humans and research animals on a whole body basis is providing researchers with an excellent tool for developing liposome‐based drug delivery agents. The attachment of therapeutic radionuclides to liposomes also has great promise in cancer therapy. Recent developments in the use of liposomes carrying therapeutic radionuclides for cancer therapy will also be reviewed. Many of the radiolabeling and tracking technologies developed for nanosized liposomes will also be useful for the imaging and tracking of other nanoparticles. Copyright © 2008 John Wiley & Sons, Inc.This article is categorized under:Diagnostic Tools > In Vivo Nanodiagnostics and Imaging