The author investigated in a group of 224 patients selected at random (380 extremities), indicated for different reasons for examination of the venous system of the lower extremities by coloured duplex and triplex sonography, the prevalence, site and clinical manifestations of deep venous insufficiency. Only 21.1% patients indicated for examination on account of clinical signs of deep venous thrombosis had objective signs of the disease, while almost half (47.7%) suffered from venous insufficiency. Venous insufficiency was detected also in a large percentage (59.9%) of patients without clinical symptoms. In the great majority of patients (99.8%) combined insufficiency was found affecting concurrently the femoral and popliteal vein and sometimes also the iliac vein.