The important radiographic and dosimetric performance parameters associated with computerized tomography (CT) are discussed together with the practical problems encountered when they are being evaluated. The parameters include alignment, slice thickness, noise, low-contrast detectability, spatial resolution, modulation transfer function and patient dose. A set of phantoms for determining these performance characteristics are described. The phantoms are of modular construction permitting measurement of the performance parameters at various sites within a number of 6 cm thick, regular-geometry, and realistic body sections. The regular-geometry sections include 20 cm diameter (skull size) and 33 cm diameter (abdomen size) sections. The realistic anthropomorphic sections include the skull, abdomen and thorax.