To investigate prospectively with color flow duplex (CFD) sonography the incidence of pseudoaneurysm or arteriovenous fistula (AVF) after transfemoral arterial catheterization with angiography, percutaneous transluminal angioplasty (PTA), or local lysis (LL). CFD sonography was used to examine the puncture site in 565 consecutive patients who had undergone PTA, LL, or angiography (581 procedures). The incidence of pseudoaneurysm in the first 300 procedures in which standard compression was used was 14.0% overall, 27.0% after LL with antegrade-puncture PTA, 18.5% after antegrade-puncture PTA, 9.3% after retrograde-puncture PTA, and 1.2% after angiography. To decrease the high incidence, in the next 281 procedures manual compression was continued for at least 5 minutes after local bleeding had stopped. This significantly reduced the incidence to 1.1% overall, 8.0% after LL in combination with PTA, 0.9% after antegrade PTA alone, 0.9% after retrograde PTA, and 0% after angiography (P < .01). The incidence of pseudoaneurysm after transfemoral arterial catheterization depends on the type of intervention. The main risk factor is too brief a period of manual compression.