Introduction and objectives. Although bundle branch block (BBB) is regarded as a frequent finding, data on its prevalence are scarce in the general population and nonexistent in patients on dialysis. The aims of this study were to determine the prevalence of complete BBB in patients starting dialysis, to identify factors associated with its presence and, secondarily, to explore its association with mortality and the occurrence of cardiovascular events. Methods. The study involved patients who started dialysis at our institution between November 1, 2003 and December 31, 2006. All underwent cardiological evaluation at the start of treatment. The presence of BBB was determined and its relationship with clinical factors and biochemical and echocardiographic parameters was examined. Patients were followed up until November 30, 2007. Results. The study included 211 patients (age 65.05±15.7 years; 56.4% male). Of these, 24 (11.4%) presented with BBB: 6 (2.8%) with left BBB and 18 (8.5%) with right BBB. Age (odds ratio [OR]=1.05; 95% confidence interval [CI], 1.008-1.113; P=.02) and body mass index (OR=1.12; 95% CI, 1.019-1.234; P=.02) were independently associated with BBB. During a mean follow-up period of 23.7±12.9 months, patients who presented with left BBB showed a clear trend towards a poorer outcome than those without a conduction defect. Conclusions. The prevalence of BBB was high in patients starting dialysis and greater than that observed in the general population. Its presence was independently associated with older age and obesity. During the mean follow-up period of 2 years, patients with left BBB demonstrated a trend towards a poor prognosis.