To determine whether complex cardiovascular interventional procedures (including coronary stent implantation, directional atherectomy, aortic valvuloplasty, and the use of an intraaortic balloon pump or cardiopulmonary bypass support) are associated with an increased likelihood of vascular access site complications, 2,400 consecutive cardiac catheterization procedures were prospectively screened over a 12-month study period. Complications occurred in 35 patients after 39 procedures (1.6%) and included the need for vascular surgical repair (17 patients), blood transfusion (28 patients) and systemic antibiotic therapy (7 patients). The incidence of complications after 1,519 diagnostic studies was 0.6%, after 698 conventional coronary balloon angioplasties 2.6%, and after 183 complex interventions 6.0% (p less than 0.0001); 43% of the complications occurred after procedures of greater than 2 hours' duration and 14% occurred in patients in whom arterial sheaths remained in situ for greater than 24 hours. Detailed demographic and procedural characteristics were compared between the 35 patients with vascular complications and 150 patients randomly drawn from a computerized database of the uncomplicated procedures performed during the screening period. By univariate analysis with correction for multiple comparisons, variables predicting the likelihood of vascular complications included: periprocedural use of heparin (p less than 0.001) or fibrinolytic therapy (p less than 0.001), arterial sheath size greater than or equal to 8Fr (p less than 0.001), patient age greater than or equal to 65 years (p = 0.01), and the presence of peripheral vascular disease (p = 0.03). The results of this study suggest that the overall incidence of access site complications is low but increases with the use of complex cardiovascular interventional procedures.(ABSTRACT TRUNCATED AT 250 WORDS)