Radiofrequency (RF) catheter ablation has developed into a new non-pharmacological therapy for the definitive treatment of patients with cardiac arrhythmias. Although an increasing number of recent reports have indicated the widespread use of the procedure, no data are available to estimate the number of procedures performed in Europe. Furthermore, currently no data on a large series of patients are available that provide information on the risk of procedure-related complications. This report presents the results of the Multicentre European Radiofrequency Survey (MERFS) that was conducted by the Working Group on Arrhythmias of the European Society of Cardiology. The objectives of this voluntary retrospective survey were to assess the number of radiofrequency catheter ablation procedures performed in 86 European institutions from January 1987 until March 1992 and the incidence of procedure-related complications with respect to the different types of ablative procedures. A total of 4398 patients were reported on from 68 out of 86 institutions (79%) from 15 European countries that agreed to participate in MERFS. From 1987 to 1991, the number of patients who underwent RF ablation per year increased from 45 to 2000. In the first 3 months of 1992, a total of 1640 patients were reported on. The number of patients reported on in relation to the different types of ablative procedures were: ablation of atrial tachycardialatrial flutter: n = 141 (3.2%); ablation of the atrioventricular junction: n = 900 (20.5%); modification of the atrioventricular junction in atrioventricular nodal reentrant tachycardia: n = 815 (18.5%); ablation of accessory pathway: n = 2222 (50.5%); ablation of ventricular tachycardia: n = 320 (7.3%). Procedure-related complications occurred in 223 patients (5.1%). The incidence of complications in relation to the ablative procedure was: ablation of atrial tachycardia/atrial flutter: 5.0%; ablation of the atrioventricular junction: 3.2%; modification of the atrioventricular junction in atrioventricular nodal reentrant tachycardia: 8.0%; ablation of accessory pathway: 4.4%; ablation of ventricular tachycardia: 7.5%. Complications occurred significantly more often in patients who underwent modification of the atrioventricular junction in atrioventricular nodal reentrant tachycardia, when compared to ablation of the atrioventricular junction (P < 0.001) or ablation of accessory pathway (P < 0.001), and in patients who underwent ablation of ventricular tachycardia, when compared to ablation of the atrioventricular junction (P < 0.002) or ablation of accessory pathway (P < 0.02). The highest incidence of complications was reported after modification of the atrioventricular junction in atrioventricular nodal reentrant tachycardia.(ABSTRACT TRUNCATED AT 400 WORDS)