Deep venous thrombosis: longitudinal study with duplex US. Forty-nine patients with deep venous thrombosis (DVT) of the lower limb were studied with repeated duplex ultrasound (US) for at least 1 year or until the vein became normal at US. Standard anticoagulant therapy was given for 3 months. In 36 patients, the veins became normal within 1 year. The likelihood of normalization increased if the lesion was located in only one site, if the pelvic veins were unaffected, if the affected leg was the left one, if the initial clot was nonocclusive, if there was no history of DVT, and if the symptoms had lasted less than than 24 hours. The average time before normalization was shorter if the symptoms had lasted less than 24 hours, that is, 11 weeks versus 25 weeks (P less than .02). The rate of sequelae at 1 year was lower if the US scan was normal or showed regression at 3 months, 6% versus 83% (P less than .00005). 