It is well known that patients with deep vein thrombosis (DVT) constitute a risk group for development of pulmonary embolism. However, the relation of DVT and the extent thereof with the subsequent sequelae (post-thrombotic syndrome) are insufficiently investigated. We have prospectively studied a series of consecutive patients admitted because of DVT on lower limbs, trying to correlate venographic findings during acute DVT with post-thrombotic (PTS) symptoms that develop later. Seventy-nine patients (84 limbs) with acute DVT were followed-up in our out-patient clinic at 4-monthly intervals for 3 years. At each visit patients were carefully examined regarding the appearance of PTS symptoms and/or signs from the DVT-affected leg. Three years after discharge, presence of PTS signs was assessed according to a simple scoring system. And then correlated to venographic findings during acute DVT. Patients were classified as having no (37 legs), mild (30 legs), or severe PTS signs (17 legs). Patients with popliteal vein involvement showed a significantly higher incidence of PTS 3 years later (P < 0.001). The risk of PTS also increased as DVT extent increased (P < 0.001). Nevertheless, the logistic regression analysis showed that DVT location explained all the differences (P < 0.001). In other words, DVT extent was overriden by the significance of DVT location, being popliteal the only location that showed a relevant contribution to the PTS incidence (95% confidence interval = 2.49-71.5).