Experience using ultrafast CT in the diagnostic evaluation of more than 50 infants and children indicates that this new technique is highly accurate and easily performed. Ultrafast CT offers several advantages compared to conventional CT. Scan times of either 0.05 or 0.1 seconds were sufficiently short to eliminate motion artifacts, even without patient sedation; sedation is a routine procedure for the conventional CT examination of most infants and small children and carries a finite risk. Procedure time appears to be shorter using ultrafast CT, 15 minutes or less, than with conventional CT. No control data using conventional CT are available for this patient population, but generally pediatric body CT studies are scheduled at hourly intervals at our medical center and are rarely completed in less than 30 minutes. Dynamic imaging alternatives for evaluation of the pediatric heart and airway include angiocardiography, digital subtraction studies, and fluoroscopy, which are limited by relatively high radiation exposure and by the inability to display all wall motions simultaneously due to their projectional rather than tomographic orientation. The potential for acquiring serial 0.05-second images of rapidly moving structures, including the heart, airway, and lungs, is unique to the ultrafast CT technique and facilitates the identification of functional abnormalities, including intracardiac shunts, valvular obstructions, tracheomalacia, and segmental bronchial obstruction. The relationships of mediastinal soft tissue structures and vessels are well defined by both ultrafast and conventional CT. In situations in which fine spatial resolution is pivotally important, the radiologist has the option with the C-100 scanner to select the 0.1-second scanning mode. This mode results in a higher radiation exposure per slice, approximately two-fold, and also uses an array of more closely spaced detectors, 864, to increase dose efficiency and spatial resolution. Although not generally required for our pediatric patients, one has the additional option of performing repeated 0.1-second images at any level, as many as ten exposures, totaling 1.0 seconds, to increase photon flux and increase resolution. Thus, the choice of scanning options can markedly influence both radiation dose, resolution, and contrast sensitivity characteristics.