Fused images of nuclear medicine (SPECT) and CT overcome the inherent limitations of both modalities of CT and SPECT. Valuable physiologic information benefits from a precise topographic localization. Coregistered data have been shown to be useful in the evaluation of patients with cancer at diagnosis and staging, in monitoring the response to treatment, and during follow up, for early detection of recurrence. The development of the new technology of single photon emission computed tomography/CT that allows for combined functional and anatomic data acquisition has the potential to make fusion an everyday clinical tool.The role of integrated SPECT/CT is growing, especially in oncologic applications. CT coregistration results in higher specificity as well as sensitivity of scintigraphic findings and markedly reduces the number of indeterminate findings. The superiority of SPECT/CT over planar scintigraphy or SPECT has been clearly demonstrated for the imaging of neuroendocrine cancer. Combining SPECT with CT in a single device has further enhanced the unquestionable role of nuclear medicine imaging in the identification and characterization of many different disorders. Advantages deriving from the use of such hybrid equipments are dual: (1) improved correction for attenuation in single photon emission tomography and (2) improved accuracy in identifying the anatomical site and extent of disease. These effects translate mostly into increased specificity (an especially worthy feature considering that relatively low specificity is a traditional drawback of radionuclide imaging), therefore into increased overall accuracy of diagnostic nuclear medicine procedures.