Despite considerable progress in the diagnosis and treatment of deep vein thrombosis (DVT) of the lower extremities, one of every three patients will develop postthrombotic sequelae within 2 years; these sequelae are severe in ~20% of cases and produce considerable socioeconomic consequences. Among factors potentially related to the development of the postthrombotic syndrome (PTS) are older age, obesity, insufficient oral anticoagulant therapy, and recurrent ipsilateral thrombosis. Whether the extent and location of the initial thrombosis are associated with the development of PTS is controversial. Based on recent findings, the lack of vein recanalization within the first 6 months appears to be an important predictor of PTS, whereas the development of transpopliteal venous reflux is not. The diagnosis of PTS can be made on clinical grounds for patients with a history of DVT. The combination of a standardized clinical evaluation with the results of compression ultrasonography and Doppler ultrasound helps diagnose or exclude a previous proximal vein thrombosis. According to the results of recent clinical studies, the prompt administration of adequate compression elastic stockings in patients with symptomatic DVT has the potential to reduce the frequency of late PTS development by half. The management of this condition is demanding and often frustrating. However, when carefully supervised and instructed to wear proper elastic stockings, more than 50% of patients will either remain stable or improve during long-term follow-up. Clinical presentation helps predict the prognosis; the outcome of patients who refer with initially severe manifestations is more favorable than that of patients whose symptoms deteriorate progressively over time.