Through clinical and venographic study of 353 diseased limbs, the authors advocate a new classification for the postthrombotic syndrome of the deep veins of the lower extremity. The postthrombotic lower extremities may be divided into two types: (1) lesions of the whole lower extremity, consisting of the completely obstructed, partially recanalized, and completely recanalized types; (2) local lesions, such as segmental obstruction of the iliac, iliofemoral, superficial femoral, femoropopliteal veins, and the tibioperoneal venous trunk and the venous plexus in calf muscles. Each type has its characteristics related to the duration of symptoms and clinical features, and their management is not the same at all. The authors suggest that clinically this new classification may be of great help in estimating the status of the diseased limb and in selecting proper method of treatment.