We investigated 76 patients with carotid sinus syndrome followed over a time period of 12-40 months (mean 24 months). In 27 patients long-term ECG were recorded over 24 hours continuously. Carotid Doppler sonography was performed in all patients. 14 patients were studied electrophysiologically. The long-term ECG examinations in patients with carotid sinus syndrome showed a significant tendency to nocturnal bradycardia, and normal heart frequency during the day. In 41% of patients extracranial obstruction of internal carotid arteries could be demonstrated. During carotid sinus massage was a significant increase of the AH time, but there was no significant changes of the HV time. 12 out of 14 patients (86%) developed an AV-block during carotid sinus massage and atrial pacing. In 31 patients pacemakers were implanted. The indication for pacemaker implantation was the clinical symptom of syncope. These patients were observed over a period of 15-40 months (mean 24 months). 15 patients were free of symptoms after the pacemaker implantation, whereas 8 patients complained of dizziness and 4 patients experienced TIA's. 45 patients without pacemaker implantation were observed over a time period of 12-24 months. 30 patients were followed over 12 months. 16 patients were free of symptoms, 14 complained of dizziness. There was no syncopy in this group and no patients died during the observation period. In patients with cardio inhibitory carotid sinus syndrome and syncopy, pacemaker implantation is the therapy of choice. In asymptomatic patients or patients with occasional dizziness pacemaker is not indicated.