Specifying and evaluating the performance of a computed tomographic (CT) scanner is necessary in order to ensure that a “typical” level of performance is achieved as well as providing baseline values for a program of quality assurance. Performance to be specified and tested include parameters related to: (a) slice geometry, (b) patient dosage, (c) artifactual behavior and (d) contrast–detail performance. Measures of performance are defined and specified. Tests which provide for performance evaluation in these four areas are detailed and discussed.