A firm diagnosis of pulmonary embolism (PE) to prevent over- or undertreatment requires an integrated use of ventilation-perfusion lung scintigraphy (V/Q scan), a recent chest X-ray, bilateral selective pulmonary angiography and venous studies. The V/Q scan should be reported in terms of probabilities according to defined criteria and be combined with clinical probabilities before a treatment decision is made. A negative V/Q scan, a low-probability scan combined with low clinical suspicion or a high-probability scan with a high clinical suspicion is generally conclusive. Patients with intermediate (indeterminate) scan probability or with discordant scintigraphic clinical probability need further work-up with pulmonary angiogram or venous studies. If neither scintigraphy nor pulmonary angiography is available, accurate venous studies of the lower legs may guide treatment decision in patients suspected of having PE. We need more research to define if all patients with PE but only a minor or no clot burden proven by venous studies really need treatment.