Purpose: A large multicenter study has recently questioned the overall clinical efficacy of vena caval filters, especially when inserted prophylactically, because of the subsequent development of deep venous thrombosis (DVT) at the insertion site. We examined the incidence of this complication with newer, smaller diameter percutaneous devices. Methods: We reviewed our vascular surgery and interventional radiology clinical registries to identify patients in whom a femoral percutaneous vena caval filter had been placed from 1993 to 1998. This list was cross referenced with patients who had undergone lower extremity venous ultrasound scan examinations for the diagnosis of DVT in the vascular laboratory within a 60- day period before and after the insertion of the filter device. Results: A total of 35 patients during this 5-year period had timely follow-up venous duplex scan studies performed. The indications for filter placement were DVT in 16 patients (46%), pulmonary embolus in 13 patients (37%), DVT and pulmonary embolus in three patients (9%), and prophylactically in three patients (9%) at high risk for thromboembolization. Of the patients with documented thromboembolic events, 91% (29 of 32) had contraindications to anticoagulation therapy, and the remaining 9% (3 of 32) represented failure of anticoagulation therapy. A Greenfield filter was used in 13 patients (37%), a Simon Nitinol filter was used in 11 patients (31%), and a VenaTech filter was used in nine patients (26%). The other two patients (6%) had a Bird's Nest filter inserted. At a mean follow-up period of 12 ± 2 days (median, 6 days), there was a 40% (14 of 35) incidence of proximal DVT in venous segments without evidence of thrombus before filter insertion. The majority (71%; 10 of 14) occurred in the common femoral vein, with three located in the superficial femoral vein and one in the external iliac vein. The lowest incidence of DVT was seen with the Greenfield and Bird's Nest filters as compared with the smaller Simon Nitinol and VenaTech filters (20% vs 55%; P < .05). The highest incidence of thrombosis occurred in patients with pre-insertion pulmonary emboli (50%; 8 of 16) as compared with those patients with DVT (38%; 6 of 16) and prophylactic insertion (0%; 0 of 3). However, the subgroups were too small to attain statistical significance. Conclusion: There is a continuing and significant incidence of new DVT development ipsilateral to the percutaneous femoral insertion site of vena caval filters. The smaller diameter filters are not associated with a lower incidence of femoral thrombosis.