Right bundle branch block (RBBB) is the most common electrocardiographic abnormality in heart transplant recipients, but the cause remains unknown, data regarding the prognosis are conflicting, and all previous studies have been limited to <100 patients. This was a study of patients who underwent heart transplantation at Stanford University Medical Center from 1981 to 1995 with known outcomes and ≥2 available electrocardiograms (ECGs). Outcomes were assessed in those with and without conduction disturbances recorded from the ECGs closest to the time of transplantation and the most recent ECGs. Of the 322 heart transplant recipients studied, 141 (44%) died over a mean follow-up of 9 ± 3.5 years, and 40 (13%) died of sudden cardiac death. In the first ECG obtained, a mean of 1.8 ± 2.4 years after transplantation, 44 patients (14%) had incomplete RBBB and 26 (8%) had RBBB; in the second ECG, obtained a mean of 5.6 ± 3.7 years after transplantation, 59 patients (18%) had incomplete RBBB and 63 (20%) had RBBB. Increasing time from transplantation was associated with a greater likelihood for RBBB on the first and second ECGs (p = 0.001 and p <0.0001, respectively). QRS duration, incomplete RBBB, RBBB, or the development of RBBB was not associated with mortality or sudden cardiac death. In conclusion, although RBBB was the most common electrocardiographic abnormality in our study, the prevalence was lower than previously reported. The cause of RBBB appears to be largely related to events that occur well after transplantation, and the prognosis is benign.