Diagnosis and management of the patient with pulmonary embolism remains a vexing clinical problem. Emboli are often unsuspected clinically. Ventilation-perfusion (VQ) scintigraphy is known to miss some emboli found on pulmonary angiography. Some physicians recommend diagnostic approaches in which the lung scan plays a relatively minor role, and angiography is required for many patients. Major prospective studies recently have made available objective data for formulation and evaluation of diagnostic and therapeutic strategies. These data suggest that the lung scan is a better predictor of patient outcome than has been previously appreciated. The goal of V/Q scanning is not detection of pulmonary emboli per se, but rather the identification of patients at a high or low risk for future embolic events if they are not anticoagulated. Several studies have shown that some emboli found on angiography are clinically benign and, in the absence of persistent thrombosis of the lower extremities, do not require anticoagulation. Treatment trials and clinical follow-up studies have shown that although the V/Q scan is not always predictive of angiogram results, it is a reliable predictor of patient outcome. In the absence of deep vein thrombosis, the low-probability scan identifies a patient population not requiring anticoagulation. When combined with objective studies of the venous system, the ventilation-perfusion lung scan provides a guide to management in the great majority of patients. Pulmonary angiography is required only occasionally.