The Authors have re-examined their case histories of 1503 patients who have had 2459 pacemakers implanted and who have undergone check-ups as outpatients. All the complications which have arisen from 1967 to the present have been taken into consideration. The total number of complications has been found in 355 patients with 14% of the total number of pacemakers and they have been subdivided into 3 groups: 1st group: complications arising during the stay in hospital (110); 2nd group: complications arising after discharge from hospital and discovered by the patient (239); 3rd group: complications found casually during outpatients' check-ups (6). Of the complications found after discharge, 97% belong to the second group and only 3% to the third group. 657 substituted pacemakers have also been taken into consideration with the purpose of finding out the parameters which showed up as the battery was running down. Out of 145 pacemakers substituted because of flat batteries, 130 (90%) have shown brusque variations in the frequency of stimulation, while only 15 (10%) have shown variations in other parameters (width, length of impulse, etc). The Authors therefore retain that a periodic outpatients' check-up of the pacemakers is of little use as regards the patients' safety and the complete utilization of the device, while they advise that the patient be educated so as to be able to carry out his own daily control of the pacemaker.