The Danish Pacemaker Register was established in January 1982, and the 11 implanting centers in Denmark report to the Register on a continuous basis by use of the European Pacemaker Patient Identification Card proposed by the European Working Group on Cardiac Pacing. As of May 1994, the Register contained data on 18,053 lead implants performed in Denmark, i.e., 1,253 (7%) lead implants before 1982, and all the 16,800 initial lead implants since 1982 on 17,020 generators in 15,366 patients for a total of 12,188 (67.5%) ventricular unipolar, 3,178 (17.6%) ventricular bipolar, 1,316 (7.3%) atrial unipolar, and 1,371 (7.6%) atrial bipolar leads. Preformed J shaped leads were used in 3.5% of the atrial implants and active fixation in < 8%. Lead failure was defined as need for replacement or abandonment of the lead due to pacing or sensing problems with the exception of lead displacement. The 10-year survival rate for unipolar atrial and ventricular leads was 95.8% +/- 2.1% (2 standard errors) and 97.1% +/- 0.6%, respectively, as compared to a 4-year survival rate of 91.5% +/- 4.6% and 91.6% +/- 1.7% for bipolar atrial and ventricular leads, and an 8-year survival rate for bipolar ventricular leads of 75.1% +/- 5.0%. The 5-year survival rate for the bipolar Medtronic model 4012 lead was 85.8% +/- 8.1% and 67.4% +/- 7.3% for the bipolar Siemens model 1010T lead, indicating a poor performance. The Siemens lead models 105T and 1050T seem to be performing like the model 1010T. The 5-year survival rate for the bipolar Telectronics model 284 lead was 88.4% +/- 6.2%. The data from the Danish Pacemaker Register confirm the previous reported good survival of unipolar pacing leads irrespective of the chamber paced, and demonstrate that the bipolar Medtronic 4012 lead, the bipolar Telectronics 284 lead, and especially the bipolar Siemens 1010T, 105T, and 1050T models are unreliable leads that need careful monitoring and appropriate replacement.