Advances in gamma-camera design over the last 5 to 10 years have improved all aspects of image quality, particularly for tomographic imaging. As system complexity increases, it becomes more important that both the technologist and physician be able to recognize the various types of artifacts that can occur in gamma-camera systems and their potential impact on clinical studies. A thorough evaluation of the system at installation and a comprehensive quality control program will detect most problems that can occur. The most sensitive indicator of gamma-camera performance is uniformity. Because this measurement is performed on a daily basis, it is the principle tool in evaluating the status of the gamma-camera. Most artifacts related to the integrity of the detector head, computer system, and hard copy device can be detected on the uniformity image. For tomographic imaging, a quantitative determination of uniformity is needed to ensure that the system will not introduce ring artifacts into the patient data. Unlike planar imaging, the complex nature of tomographic imaging requires additional checks on system performance to ensure that other components of the system, such as the collimator, gantry, and imaging table, are not a source of artifact in the reconstructed image data. Failure of a system component can occur at any time and may be subtle and difficult to recognize in modern systems. In such an environment it becomes imperative that any unexpected finding in a clinical study be questioned with respect to a possible malfunction of some aspect of data acquisition and analysis.