Pulmonary embolism (PE) should be suspected in patients with dyspnea, chest pain, syncope, shock/hypotension, or cardiac arrest. Discriminating patients in different categories of pre-test probability of PE has become a key step in all diagnostic algorithms for PE. The most frequently used clinical prediction rule is the Wells score ("PE likely" > 4 points and "PE unlikely" ≤ 4 points). PE can be safely ruled out in patients with a "PE unlikely" associated with a negative d-dimer test result. Conversely, patients with "PE likely" or positive d-dimer level should undergo further diagnostic testing, like multidetector computed tomography pulmonary angiography (MCTPA).