Evolution of deep venous thrombosis: a prospective evaluation with US. Forty-six patients with a diagnosis of acute deep venous thrombosis (DVT) established by means of duplex ultrasound (US) were prospectively followed up with serial duplex US examinations during a 6-month period to assess the persistence of venous abnormalities. All patients were asymptomatic. Isolated popliteal DVT was found to be more likely to revert to normal at duplex compression US than thrombosis involving both the femoral and popliteal systems (P less than .05). Increased venous diameter was a sign of acute clot (P less than .005). Clot echogenicity did not help to enable distinction of acute DVT and chronic DVT. At compression US, 10 of 21 patients (48%) who initially had occlusive thrombosis had persistent abnormalities that mimicked findings consistent with acute DVT. Chronic venous changes that persisted after 6 months consisted of either lumen recanalization (with resultant intimal thickening) or persistent venous occlusion. Both of these conditions can result in incomplete compression, the major US indication of acute DVT. This appearance should not be confused with that of acute DVT. Follow-up examinations to establish a baseline appearance can be obtained as early as 6 months after an acute episode of DVT. 