Recently a debate has developed in the medical community as radiologists in some centers suggest the selective substitution of spiral computed tomography (CT) for ventilation-perfusion (V/Q) nuclear medicine imaging as a screening test for the diagnosis of acute pulmonary embolism. Proponents of spiral CT argue that it is more accurate than the usual practice of combining the (V/Q) scan and the physician's best clinical judgment. V/Q scans classify patients into groups according to the probability of pulmonary emboli, whereas the thrombus is visible with spiral CT. Opponents point out that large-scale patient outcome studies using spiral CT have not been completed, but such information is available for (V/Q) scans. Most clinicians are familiar with the strengths and limitations of an assessment that relies primarily on the (V/Q) scan, because this examination has been available for many years. Although spiral CT does not perform as well as pulmonary arteriography in detecting subsegmental emboli, the importance of smaller peripheral emboli is controversial. This review explores the advantages and disadvantages of investigations currently available for the diagnosis of acute pulmonary embolism from the perspective of the emergency physician, presenting the view that spiral CT is likely to have an increasingly important place in patient evaluation.