Both false-positive and false-negative diagnoses are common. To avoid errors in either direction, knowledge of risk factors and of the applicability of various tests is crucial.Paradoxically, pulmonary embolism is underdiagnosed and overdiagnosed, i.e., both false-negative and false-positive diagnoses are common. To avoid errors in either direction, knowledge of risk factors is crucial, as is knowledge of the appropriate applicability of various clinical and laboratory procedures. In a vast majority of cases, minidose heparin prophylaxis remains the mainstay of management.