In order to help clarify the long-term results of filter implantation and how best to manage the post-operative care, 92 patients with implanted filters were observed for up to 6 years. The follow-up examinations included detailed interrogation, a clinical investigation, plain abdominal radiography in two planes, contrast-enhanced computed tomography of the vena cava and colour-coded duplex sonography of the vena cava and the veins of the pelvic and legs. In the early phase of the study, two patients who received Günther filters in 1988 experienced dislocation of the filter after 3 months. In the later phase, 85% of those treated with oral anti-coagulants and compression showed patent pelvic veins in areas where, at the time of filter implantation, there had been thrombi with the potential to cause embolism. In 72 cases, the inferior v.cava proved to be patent in the area of the filter.