The authors describe the fatal illnesses of three Byzantine emperors, Alexander, Michael IX Palaeologus and Manuel II Palaeologus, who may have died of a stroke. From the texts of Byzantine historians and the indications of chroniclers, it was found that Alexander died of a stroke (possibly cerebral hemorrhage); Michael IX Palaeologus died of what seems to have been the same disease and the the last of these emperors, Manuel II Palaeologus, of hemiplegia. This paper provides the opportunity to see how the non-medical texts of historians and chroniclers adopt and express the scientific Byzantine terminology of the medical writers of the period, which is used differently today.