In the past century, the field of psychiatry has undergone major changes. During this time, significant advancements in both diagnosis and treatment have occurred. Medical brain imaging using structural and functional brain imaging techniques have contributed, in part, to a better basic understanding of psychiatric disease and to an improving diagnostic approach. Computed tomography and magnetic resonance imaging have supplied limited, but useful insight regarding structural alterations in schizophrenia and the affective disorders. Position emission tomography imaging has already made a major contribution in the assessment of schizophrenia and affective disorders. Single-photon emission computed tomography (SPECT), which is currently more widely available, should contribute more to psychiatric disease evaluation in the future. Recent advances in SPECT technology in the areas of improved instrumentation--such as multidetector and ring detector systems and new radiopharmaceuticals including new rCBF markers and receptor site imaging agents--have contributed to significant improvements in the SPECT imaging technique. At the present time, SPECT has been shown to be feasible and useful in the evaluation of acute and chronic psychiatric and demented states. As SPECT technology continues to evolve, further refinements in this diagnostic capability can be anticipated.