AbstractA wide range of clinical symptoms and signs are observed with venous thrombosis. Nonetheless, clinical diagnosis has been found to be unreliable and accurate diagnostic methods must be used before potent therapy such as anticoagulation is instituted, since the complications of treatment themselves can be life‐threatening.Phlebography is still the basic reference for evaluation of deep venous disease. While it is felt to be the most accurate, there are still limitations relative to difficulty in separating acute from chronic disease, and in obtaining adequate contrast in certain veins such as calf muscles and in the larger intraabdominal veins. Moreover, it is an uncomfortable invasive test, not without complications of its own.The125I‐fibrinogen uptake test is an excellent test for screening for forming thrombi. The sensitivity of this test is high, particularly in the detection of small calf vein thrombi. The primary drawbacks of this technique are that it is falsely positive in cases where there has been bleeding, inflammation, gross edema, arthritis, or leg ulceration. It is not accurate above mid‐thigh because of the high blood flow at the level of the groin and pelvis.Radioactive labeled plasmin which will adhere to the surface of recently formed thrombi can also be used for diagnosis. The limitations are a very short half‐life of the radioactive label so that repeated investigation of a patient cannot be performed unless new injections are given. The diagnostic accuracy is comparable to that of radioactive labeled fibrinogen and has the same advantages and disadvantages.Plethysmographic techniques have been used with various modifications. They have the advantage of being strictly noninvasive. They are most accurate when used in association with venous emptying, but there must be at least 50% occlusion of the vein before the test is positive and large collaterals or duplication anomalies may result in a false‐negative test. Phleborrheography seems to diagnose proximal deep venous disease accurately, but is relatively insensitive to distal deep venous thrombosis. Doppler ultrasound techniques are quick and simple to apply, but interpretation requires substantial experience.Real‐time B‐mode ultrasound has been used in recent years to detect deep venous thrombosis and permit visualization of thrombus within a vessel. With experienced hands, it is possible to differentiate between acute and chronic thrombi.Finally, a combination of 2 or more methods has been found to increase diagnostic accuracy; combining one method which is good at detecting calf vein thrombosis with one detecting hemodynamically significant thrombi in the more proximal veins offers the best combination. Impedance plethysmography combined with radioactive labeled fibrinogen has been found to be nearly as reliable as phlebography with similar cost effectiveness.