We performed a formal decision analysis to evaluate the cost-effectiveness of various strategies for pulmonary embolism, including helical computed tomography (CT), and determined the most cost-effective schemes for each clinical probability of pulmonary embolism. Other tests included D-dimer (DD), lower limb venous ultrasound (US), ventilation-perfusion (V/Q) scan, and angiography. Outcome measures were 3-month survival and costs per patient managed. Baseline sensitivity of CT was 70%, corresponding to the performance of single-detector CT, and that figure was raised in sensitivity analysis to account for the expected higher sensitivity of newer multidetector CT scanners. All strategies were compared with a reference strategy, namely the V/Q scan in all patients followed when nondiagnostic by an angiogram. For low clinical probability patients, the most cost-effective strategy was DD, US, and V/Q scan, patients with a nondiagnostic V/Q scan being left untreated. Replacing V/Q scan by CT was also cost-effective. For intermediate and high clinical probability patients, a fourth test must be added, either CT or angiography in patients with nondiagnostic V/Q scan, or angiography in patients with a negative helical CT. When using sensitivity figures above 85% (in the multidetector range), DD, US, and CT became the most cost-effective strategy for all clinical probability categories. Helical CT as a single test was not cost-effective. In summary, including helical CT in diagnostic strategies for pulmonary embolism is cost-effective provided that it is combined with DD and US. In contrast, helical CT as a single test is not cost-effective.