In recent years, non-invasive sonographic techniques [real-time ultrasound (US), duplex ultrasonography (DU) and color-coded duplex sonography (CCDS)] have increased in importance for the diagnosis of lower extremity deep venous thrombosis. To ascertain the accuracy and limitations of these techniques prospectively, various studies have been performed to compare sonography with venography. This review deals with basic methodologic considerations when two imaging methods are compared and describes the features of deep venous thrombosis seen on US, DU and CCDS. Reports comparing sonography and phlebography for the diagnosis of deep venous thrombosis are presented and discussed. The advantages and limitations of US, DU and CCDS for the diagnosis of iliac, femoral, popliteal and infrapopliteal venous thrombosis are compared with those of venography, and controversial areas are touched on.