In a previous retrospective treatment-comparison study of 168 patients with sinus node disease, we found a significantly higher incidence of permanent atrial fibrillation and congestive heart failure in patients treated with ventricular (VVI) pacing compared to atrial (AAI) pacing, after an average follow-up period of 2 years. To determine whether these differences persisted and whether AAI pacing resulted in a lower mortality rate than VVI pacing during long-term follow-up, the treatment groups were restudied after an average of 4 years of pacemaker treatment. The incidence of permanent atrial fibrillation was still significantly higher (p less than 0.0005) in the VVI group than in the AAI group after the additional 2 years (VVI = 47%, an increase from 29%; AAI = 6.7%, an increase from 3.4%). Congestive heart failure occurred significantly more often in the VVI group than in the AAI group (37% vs 15%, p less than 0.005). Analysis of survival data showed a higher overall mortality rate in the VVI group (23% vs 8%, p less than 0.05). The development of high-degree atrioventricular block in the AAI group remained low (total 4.5%). Thus, in sinus node disease, the advantages of AAI over VVI pacing persist during long-term follow-up. The differences in cardiovascular morbidity between the groups tend to increase with time and appear to result in a lower mortality rate among patients treated with AAI pacing.