One of every three patients with deep-vein thrombosis of the lower extremities will develop, within 5 years, post-thrombotic sequelae that vary from minor signs to severe manifestations such as chronic pain, intractable edema, and leg ulceration. The post-thrombotic syndrome (PTS) develops as a result of the combination of venous hypertension due to persistent outflow obstruction or valvular incompetence and abnormal microvasculature or lymphatic function. Among factors potentially related to the development of PTS, recurrent ipsilateral thrombosis plays a major role. Whether the extent and the location of the initial thrombosis are associated with the development of PTS is still controversial. The diagnosis of PTS can be accepted on clinical grounds for patients with a history of venous thrombosis. The combination of a standardized clinical evaluation with the results of compression ultrasonography and Doppler ultrasonography helps diagnose or exclude a previous proximal-vein thrombosis. Prevention of recurrent thrombosis and use of compression elastic stockings are the cornerstones of PTS prevention. The management of this condition is demanding and often frustrating. Although several surgical procedures have been tested, conservative treatment is largely preferable, as more than 50% of patients either remain stable or improve during long-term follow-up, if carefully supervised and instructed to wear proper elastic stockings. Clinical presentation helps predict the prognosis, being the outcome of patients who refer with initially severe manifestations more favorable than that of patients whose symptoms progressively deteriorate over time.