Combined positron emission tomography (PET) or single photon emission computed tomography (SPECT) with computed tomography (CT) has been rapidly developed because of unique physiological information benefits from a precise topographic localization. PET/CT has been more accurate that anatomical imaging for diagnosing, staging, restaging and assessing therapeutic responses in a large number of different cancers. SPECT/CT has been somewhat overlooked since the procedures with single-photon tracers still constitute the majority of everyday nuclear medicine practice. Besides of precise localization of the lesions CT findings also characterize the abnormalities. Many existing and potential areas of clinical applications as well as translational researches using PET/CT and SPECT/CT are briefly reviewed.