Introduction and objectives. Patients with chronic bifascicular block (BFB) can progress to advanced atrioventricular block (AVB), especially when syncope or a prolonged HV interval is present. It is possible that other variables could help identify patients who would benefit from prophylactic pacemaker implantation. Methods. The study involved 263 consecutive BFB patients seen at a single center between 1998 and 2006. Clinical, electrocardiographic and electrophysiologic variables were analyzed to identify predictors of progression to significant AVB (i.e. second or third grade). Cardiac pacemakers were implanted in accordance with European Society of Cardiology guidelines. Pacemakers were programmed in the VVI mode with a minimum frequency of 40 beats/min. A pacemaker was required if there was significant AVB or a ventricular pacing percentage >10%. Results. In total, the study included 249 patients (mean age, 73.4±9.3 years, 82 female). After a median follow-up period of 4.5 years (2.16-6.41 years), a pacemaker was required by 102 patients: 45 had a ventricular pacing percentage >10% and 57 had significant AVB. Factors predictive of the need for a pacemaker were: the presence of syncope or presyncope (hazard ratio [HR]=2.06; 95% confidence interval [CI], 1.03-4.12), QRS width >140 ms (HR=2.44; 95% CI, 1.59-3.76), renal failure (HR=1.86; 95% CI, 1.22-2.83), and an HV interval >64 ms (HR=6.6; 95% CI, 4.04-10.80). The presence of all four risk factors was associated with a 95% probability of needing a pacemaker within 1 year of follow-up. Conclusions. The presence of syncope or presyncope, a QRS width >140 ms, renal failure, and an HV interval >64 ms were independent predictors of progression to AVB in patients with BFB.