PURPOSE: Motion artifacts of the ascending aorta may impair image quality and simulate an intimal flap or a false channel. The purpose of this study is to evaluate the prevalence, amplitude, and extent of motion artifacts of the aorta in spiral CT and to specify the effects of acquisition and reconstruction parameters on these artifacts. METHOD: One hundred seventy-one thoracic spiral CT examinations were retrospectively analyzed by two reviewers. The analysis sought to determine the presence, location, amplitude, and extent of artifacts of the ascending aorta. RESULTS: Aortic artifacts were detected on spiral CT in 57% of cases. The mean amplitude and mean extent were 4+/-4 and 6+/-7 mm, respectively. Artifacts in the ascending aorta were significantly higher with the 360 degrees linear interpolation (LI) algorithm than with the 180 degrees LI algorithm. CONCLUSION: The prevalence of motion artifacts on spiral CT is higher in this study than the reported prevalence in incremental CT. However, this higher prevalence is significantly reduced when the 180 degrees LI algorithm is used.