Despite technological progress, the clinical diagnosis of acute pulmonary embolism (APE) is often problematic, There are no typical or specific clinical cardiopulmonary symptoms or signs that serve for the diagnosis, and only the absence of tachypnea seems to be an important exclusion criterion. Electrocardiogram, laboratory tests (including circulatory markers of thromboembolic disease) and blood gas analysis are also unspecific. Chest X-ray provides a high incidence of suggestive abnormalities and remains the most helpful routine procedure. While the negative perfusion lung scan is the best procedure for exclusion of APE, the positive scan suffers from too low specificity to be of real interest. In contrast, pulmonary angiography is the diagnostic method of choice. Besides detection of pulmonary emboli and of the extent of perfusion abnormalities, pulmonary angiography allows measurement of useful parameters of cardiac and pulmonary function, precise monitoring of evolution and administration of selective thrombolytic therapy. The diagnostic value of recent noninvasive diagnostic procedures in APE (echocardiography, Doppler echocardiography, computer tomography, plethysmography) is briefly discussed.