Background: Post-thrombotic syndrome (PTS) is a long-term complication of deep vein thrombosis (DVT) characterised by chronic complaints such as oedema and skin changes including; venous ectasia, varicose veins, redness, eczema, hyperpigmentation, and in severe cases fibrosis of the subcutaneous adipose in the affected limb. These chronic complaints are the effects of venous outflow restriction that can cause symptoms such as heaviness, itching, pain, cramps, and paraesthesia. Twenty to fifty percent of people with DVT develop post-thrombotic complications. Several non-pharmaceutical measures are used for prevention of PTS during the acute phase of DVT. These include elevation of the legs and compression therapy. There have been limited studies regarding the effectiveness of compression therapy for prevention or treatment of PTS. As a result, clinicians and guidelines differ in their assessment of compression therapy during treatment of DVT and in the treatment of PTS. This is an update of a review first published in 2003.Objectives: To assess the effectiveness of compression therapy for treatment of post-thrombotic syndrome, including elastic compression stockings and mechanical devices compared with no intervention, placebo and with each other.Search Methods: For this update, the Cochrane Vascular Information Specialist searched the Cochrane Vascular Specialised Register, CENTRAL, MEDLINE, Embase and CINAHL databases and World Health Organization International Clinical Trials Registry Platform and ClinicalTrials.gov trials registries on 2 July 2018.Selection Criteria: We included trials that evaluated compression therapy for the treatment of PTS. The primary outcomes were severity of PTS and adverse effects. There were no restrictions on date or language. Two review authors (SA, DNK) independently assessed whether potentially relevant studies met the inclusion criteria.Data Collection And Analysis: One review author extracted and summarised data and one review author (DNK) verified them. We resolved disagreements by discussion. We assessed methodological study quality with the Cochrane 'Risk of bias' tool. We used GRADE to assess the overall certainty of the evidence supporting the outcomes assessed in this review.Main Results: We identified four trials, with 116 participants, investigating the effectiveness of compression therapy for treatment of PTS. The methodology used by each trial was too heterogeneous to perform a meta-analysis, so we reported our findings narratively.Two trials studied the effect of graduated elastic compression stockings (GECS) on improvement of PTS symptoms. One study reported beneficial haemodynamic effects, while the other found no benefits on PTS severity compared to placebo (very low-certainty evidence). There was very limited evidence available for adverse effects and quality of life (QoL). The two studies did not report on compliance rates during the study period.Two trials studied the effects of intermittent mechanical compression devices. Both reported improvement in PTS severity (low-certainty evidence). Improvement of the severity of PTS was defined by treatment 'success' or 'failure'. Only one study comparing compression devices evaluated adverse effects and QoL. Although 9% of the participants experienced adverse effects such as leg swelling, irritation, superficial bleeding, and skin itching (moderate-certainty evidence), QoL was improved (moderate-certainty evidence). Studies did not assess compliance using intermittent mechanical compression devices.None of the studies evaluated patient satisfaction.Authors' Conclusions: There is very low-certainty evidence regarding the use of GECS for treatment of PTS as assessed by two small studies of short duration. One study reported beneficial haemodynamic effects, while one found no benefits on PTS severity compared to control/placebo stockings. There is very limited evidence for adverse effects, patient satisfaction, QoL, and compliance rates. There is low-certainty evidence favouring use of intermittent pneumatic compression devices compared to a control device for the treatment of severity owing to different measurements used by the studies reporting on this outcome and small studies of short duration. There is moderate-certainty evidence of improved QoL but possible increased adverse effects related to compression device use owing to small studies of short duration. High-certainty evidence to support the use of compression therapy in prevention of PTS is lacking and any conclusions drawn from current evidence should be interpreted with care. Further research is needed to assess whether compression can result in long-term reduction and relief of the symptoms caused by PTS, or prevent deterioration and leg ulceration.