Due to the markedly increased number of arterial punctures performed during diagnostic angiography and angioplasty procedures for cardiac and peripheral vessel disease, the complication of false aneurysms after arterial puncture has gained increasing significance. The incidence of false aneurysms after puncture reported in the literature ranges from 0.05-2%. However, careful sonographic follow-up may reveal an incidence twice as high. The goal of this retrospective investigation of 28 patients with false aneurysms was to elucidate risk factors leading to failure of spontaneous closure of the arterial site, as well as to examine the symptoms and clinical course of such patients. Pseudoaneurysms became manifest, depending on the method of puncture, on average 16.4 days after the procedure. The highest risk was seen in adipose patients (18 pts., 64.3%). In these patients the number of tangential and multiple vessel punctures was also highest. Further risk factors were local vessel sclerosis, hypertension, diabetes mellitus, poor general condition, and disturbances of blood coagulation. The typical clinical findings were seen in only 13 patients. In 3 patients blood loss was the predominant symptom. Twelve further pseudoaneurysms (42.8%) were found incidentally at follow-up. The diagnosis was made in all patients sonographically. In 1 patient it was initially identified as an incidental finding at angiography. In 25 cases simple vessel reconstruction was possible (stitch or patch). In 3 cases (10.7%) a more extensive procedure involving vessel replacement was necessary. Severe postoperative complications included local infection (in 2 patients, 1 of whom also had a recurrent false aneurysm) and arterial bleeding necessitating surgical intervention (1 patient).(ABSTRACT TRUNCATED AT 250 WORDS)