The reported incidences of post-thrombotic syndrome (PTS) after deep vein thrombosis (DVT) vary. Further, PTS symptom development over time and its long-term incidence are unknown. Patients included in the MEGA study were interviewed at 1 year and completed a questionnaire at 8 years of follow-up regarding symptoms and signs of PTS based on the Villalta score after a first DVT diagnosis. The cumulative incidence of PTS at 0–1 and 1–8 year, changes in PTS classification and the effect of possible clinical and laboratory risk factors were determined. After 1 year, 361 out of 1657 patients diagnosed with DVT were classified as having PTS, for a 0–1 year cumulative incidence of 21.8% (95%CI 19.9–23.8), out of whom 92 (5.6%) had severe PTS. After 8 years 633 patients without previous PTS completed the second questionnaire, of whom 44 were classified as having PTS, for a 1–8 year cumulative incidence of 7% (95%CI 5.2–9.2); of these 13 (2.1%) were classified as severe PTS. During follow-up PTS complaints improved in 69% and worsened in 7% of patients. At 1 year, risk factors were female sex (RR 1.5; 95%CI 1.2–1.9) and obesity (RR 1.5; 95%CI 1.2–7.9), with the same effect sizes at 8 years. Provoked/unprovoked DVT, thrombus location, pregnancy, hormone use and several laboratory parameters did not affect risk of PTS, either at 1 or 8 years. The incidence of PTS remained substantial up to 8 years after a first DVT. Symptoms improved in a large proportion of the cases. The short and long term risks were highest in women and obese patients. •The incidence of and risk factors for PTS of the leg are debated.•1 and 8 years after DVT we scored patients on PTS based on the Villalta score.•0–1 and 1–8 year PTS incidences were 21.8% and 7.0% respectively.•PTS symptoms improved in 69% of patients.•Relevant risk factors for PTS were female sex and obesity (BMI > 30 kg m−2).