Incidental pulmonary embolism (PE) in cancer patients is usually thought to be of mild degree. We investigated the severity of PE and evaluated the potential of raising the suspicion of PE in such patients. The computed tomography (CT) extent of PE was evaluated in 19 consecutive unsuspected and 19 randomly selected symptomatic patients. A clinical pattern useful for suspecting PE was also searched. On CT, number of embolized vessels, location of emboli, and simple instrumental findings were not different in the two groups. PE is not less severe in unsuspected cancer patients; moreover, PE may be clinically suspected in such patients.