Following deep venous thrombosis (DVT), patients may develop leg swelling, skin changes and ulceration. Early studies have suggested that patients suffer progressive deterioration and poor eventual outcome. The objective of this study was to determine whether extensive DVT still carries a poor prognosis. In this study 83 patients with 86 affected limbs were followed with annual review for 12-135 months, median 47 months. Thirty-seven patients were referred at time of DVT and 46 patients referred with established symptoms following DVT. In the latter group, time from DVT to referral ranged from mean 2-45 years (median 7 years). All patients had phlebographically proven deep venous thrombosis. The main outcome measures were subjective improvement in symptoms, healing of leg ulcer or development of a new leg ulcer. Deterioration or improvement in signs of post-thrombotic syndrome were documented by one observer (CVR). Patients were routinely provided with graduated compression stockings. They were given advice, as appropriate, on weight reduction and care of the limb. Improvement of symptoms was reported in 25 (29%) limbs, 49 (57%) had no change and 12 (14%) deteriorated. Three patients (3%) developed a new leg ulcer. The great majority of patients following extensive deep venous thrombosis, when provided with graduated compression stockings and regularly supervised, either remained stable or improved when followed long-term. The development of a new leg ulcer was uncommon. The post-thrombotic syndrome does not carry the poor prognosis reported in earlier studies.