The last decade has seen the development of hybrid imaging technologies combining positron emission tomography (PET) or single-photon emission computed tomography (SPECT) with x-ray computed tomography (CT). Numerous studies demonstrate the superiority of PET/CT and SPECT/CT over stand-alone PET and SPECT in terms of diagnostic accuracy. For PET with (18)F-fluorodeoxyglucose (FDG), this has been demonstrated for bronchial carcinomas, high-grade lymphomas, melanomas, and head and neck tumors, to name a few. Combined imaging of structure and biochemistry is expected to be even more important for tracers such as (124)I that are more specific for tumor tissue. Similarly, SPECT/CT has revolutionized the field of conventional nuclear medicine. Available evidence indicates that this hybrid imaging technology will become the gold standard for conventional scintigraphy, including bone imaging performed for staging malignancy, and also for the so-called tumor scintigraphies that visualize neoplastic foci via tumor-specific agents such as octreotide labeled with (111)In or (131)I. Another important indication for SPECT/CT is sentinel lymph node scintigraphy, where SPECT/CT fusion helps considerably in localizing the first lymph node draining a tumor. Technological progress never stands still; hybrid cameras combining PET and MRI have already been introduced. These systems will lead medical imaging to new horizons, and they will offer the virtually unlimited potential of simultaneously acquiring morphologic, functional, and molecular information about the living human body.