Pulmonary embolism is a common clinical problem. Its symptoms and signs are inespecific and the tests commonly used are either non sensitive or non specific. Pulmonary angiography is considered as the "gold standard" for pulmonary embolism diagnosis. However, it is usually unavailable, very expensive, invasive and sometimes of complex interpretation. Thoracic helical computed tomography is a new technique, available in our clinical setting. It has become the most sensitive and specific test for pulmonary embolism detection and whose results can change our therapy. We report a clinical case with a leg thrombosis and an undoubted pulmonary embolism on clinical basis. After presenting a leg thrombosis which was confirmed by Doppler ultrasound, the patient developed bilateral pulmonary infiltrates, and bilateral pleural effusion. He did not presented fever nor elevated white cell counting in peripheral blood. The patient improved with anticoagulant therapy. He did not receive antibiotics. Nevertheless the helical computed tomography was normal. Therefore if pulmonary tromboembolism is clinically indubitable, we should be cautious in taking clinical decisions, based on a single test, no matter how efficient it is