FDG PET imaging is rapidly gaining acceptance in numerous clinical applications in oncology. PET/CT is a new imaging tool, which takes advantage of the excellent anatomic resolution of CT and the biologic characterization provided by FDG PET which together results in improvement in accuracy of detecting the extent of disease, provide a guide to biopsy or surgery, allow early response evaluation and prognostication. This article will provide specific clinical applications for the utilization of these imaging modalities in both lymphoma and melanoma.