The Danish Pacemaker Register was established in January 1982, and the 12 implanting centers in Denmark report to the Register on a continuous basis by use of the European Pacemaker Patient Identification Card. As of August 1999, the Register contained data on 33,164 bradycardia, endocardial, and epicardial (n = 159) lead implants performed in Denmark on 27,738 generators in 24,180 patients for a total of 17,988 (54.2%) ventricular unipolar, 5,610 (16.9%) ventricular bipolar, 2,056 (6.2%) atrial unipolar, and 7,242 (21.8%) atrial bipolar leads. Lead failure was defined as need for replacement or surgical abandonment of the lead due to pacing or sensing problems with the exception of lead displacement. The 10-year survival rate for unipolar leads was 97.2 +/- 0.4% (+/- 2 SE) as compared to 79.6 +/- 3.2% for bipolar leads (P < 0.001). The Medtronic 4012, the Telectronics 284, and the Siemens (Pacesetter) 1010T, 105T, and 1050T bipolar lead models were poor performing leads that needed careful monitoring and appropriate replacement. Excluding those five poor performing bipolar leads, the models yielded a 10-year survival rate of 94.3 +/- 2.4% for bipolar leads. The 5-year survival for all bipolar leads implanted after January 18, 1993 (this was the date that the last of the five poor performing bipolar lead models were implanted in Denmark) was 98.7 +/- 0.4% compared with 98.9 +/- 0.3% for all unipolar leads implanted after January 18, 1993 and 86.8 +/- 1.6% for all bipolar leads implanted on or before January 18, 1993. These results indicate a significant improvement in bipolar lead reliability.