Spiral computed tomography (CT) has recently become available as a practical diagnostic tool; its introduction has created the need for a comprehensive understanding of the magnitude and distribution of the radiation dose to the patient. Dose distributions for conventional and spiral CT were measured with thermoluminescent dosimeters loaded in standard phantoms and then compared to determine the validity of using standard dose descriptors for assessing the dose delivered during spiral CT. Two dose descriptors applied to conventional CT, the CT dose index and the multiple-scan average dose, were found to be adequate for quantifying the dose delivered by spiral CT.