The diagnosis of pulmonary embolism may be confounded by a clinical presentation that is often subtle or atypical. Therefore pulmonary angiography, although invasive, has been widely used to prove pulmonary embolism. The aim of this review is to discuss the value of non-invasive techniques, such as lung scan and chest computed tomography scan, in the diagnosis of pulmonary embolism. Ventilation-perfusion scan has demonstrated a very high specificity (97%) but a quite low sensitivity (41%) in the diagnosis of pulmonary embolism, while perfusion lung scan not associated with ventilation scan has shown a specificity of 92% and a considerably high sensitivity (87%). The chest computed tomography scan has not yet shown a definite degree of specificity and sensitivity in the diagnosis of pulmonary embolism, although we suppose that this technique will become widely used. However, we emphasize that the diagnosis of pulmonary embolism is not a mere technical problem.