Interest in clinical fluorodeoxyglucose (FDG) imaging with dual-headed gamma cameras continues to grow. In 1996, Jarritt and Acton published a review article of the use of gamma-camera systems for FDG imaging [1]. Since that article was published, considerable progress has been made in the adaptation of dual-headed camera systems for coincidence imaging. We review the basic principles of dual-headed coincidence imaging and some of the major limitations and challenges in the development of such technology. Since much of the current clinical experience with FDG imaging is based on the use of dedicated position emission tomographic (PET) systems, some comparisons of the performance limitations between dual-headed gamma-camera and dedicated PET systems are provided.