A hydrodynamic thrombectomy catheter was prospectively evaluated for the treatment of recently thrombosed vessels. A total of 52 consecutive patients (42 males and 10 females; mean age 64 +/- 15 years) presenting with acute or subacute occlusion of dialysis shunts (n = 25), peripheral bypass (n = 14) or native arteries (n = 15) were treated with the Hydrolyser (Cordis Europa NV, Roden, The Netherlands). Mean occlusion time was 4 days (range 1-17 days) and mean thrombus length 19 +/- 11 cm. The Hydrolyser was effective and fast in removing thrombus, regardless of the thrombus length. No major complications were reported. The immediate procedure success rates were 82, 100, 87 and 79 % for Brescia Cimino, dialysis shunt, native arteries and bypass grafts, respectively. Adjunctive thrombolysis (applied for persistence of residual thrombus or thrombosed distal vessels too small for hydrolytic thrombectomy) was required in 4 % of thrombotic dialysis shunts, in 20 % of native arteries and in 50 % of bypass graft occlusions. On angiographic controls, distal embolizations were reported only in native arteries (13 %) and bypasses (14 %); all were successfully treated percutaneously, except for one case treated by Fogarty balloon. Cumulative primary patency rates were respectively at 6 months 56, 62, 78 and 65 % for each indication. We conclude from this preliminary clinical study that hydrodynamic thrombectomy with a Hydrolyser is a promising technique to treat acute occlusions. This device can reduce complications as well as the time required to remove large amounts of thrombus and the use of expensive thrombolytic drugs.