A 21 year old patient was operated for bilateral ptosis and external ophthalmoplegia at 13 years of age. At this time there were no signs of retinitis pigmentosa or atrioventricular block, features of the Kearns and Sayre Syndrome (1958) which were detected five years later. His bundle recording showed an intrahisian block (1 degree proximal and a complete distal block) with a trifascicular block, the latter persisting alone during a brief return to sinus rhythm. This is one of the rare cases of the Kearns and Sayre Syndrome with documented His bundle recordings and the only reported case with intrahisian block. The patient also suffered from bilateral neural deafness. The patient's condition remains stable after implantation of an isotopic cardiac pacemaker and he now leads a normal life. A review of 52 previously published cases shows that this rare condition appears to be caused by a mitochondrial abnormality, which, for an unknown reason, affects only the neuromuscular and cardiac conduction systems. The prognosis is poor when swallowing and respiration are affected, but this does not occur in all cases. As cardiac conduction abnormalities are the other life-threatening complication, cardiac pacing has greatly improved the prognosis of these patients.