Multislice computed tomography (CT) systems are an important step forward in CT technology and will probably displace traditional single-slice systems within the next 10 years. Unlike single-slice CT, multislice can acquire two or more slices in a single rotation. This faster scanning speed allows more slices--and thinner ones--to be obtained. It also reduces or eliminates artifacts produced by patient movement and reduces the x-ray tube heating that can constrain single-slice scanning parameters. At the same time, multislice CT is more expensive than single-slice and has the potential to increase the radiation dose delivered to patients. For this Evaluation, we tested four-slice scanners from GE, Philips, Siemens, and Toshiba, examining their technical and clinical performance and their ease of use. All four products represent a considerable advance over single-slice scanners, and we rate them all Acceptable. We rank two of them higher than the others because of their suppliers' proven ability to upgrade their scanners and because of the demonstrated efficacy of the scanners' automated dose-control systems. Also in this Evaluation, we discuss just why automated dose control is so important and provide advice on deciding at what point you should acquire a multislice scanner.