Objective: To determine the incidence of catheter-related surgical emergencies during pediatric interventional catheterization procedures. Study design: We reviewed all interventional catheter procedures (n = 578) over a 4-year period (April 1996 to April 2000) to determine any complication during interventional catheterization that required surgery within 24 hours after catheterization. Results: The overall incidence of surgical emergencies was 1.9% (70% confidence limits, 1.5% to 2.7%). Complications that required surgical intervention occurred with balloon dilation (valvuloplasty, angioplasty, n = 4), device deployment (coils, stents, atrial-septal defect devices, n = 5), transhepatic access (n = 1), and atrial transseptal puncture (n = 1). For the majority of interventions, the incidence of surgical emergencies was <4% except for two procedures (conduit and pulmonary artery angioplasty) with limited numbers of patients. There were no surgical emergencies during endomyocardial biopsy, coarctation angioplasty, or balloon atrial septostomy. Conclusions: Surgery was required in 1.9% of all interventional catheter procedures. Surgical emergencies occurred during a wide variety of catheter interventions and could not be predicted by the type of procedure performed. (J Pediatr 2002;140:570-5)