Thomas Jefferson had severe headaches on a number of occasions during his adult life, as noted by most of his biographers. Some occurred during important historical events, including the period just before the writing of the Declaration of Independence. Historians generally have considered these headaches to be migraines, while some physician authors have considered the alternative diagnoses of tension-type headaches and cluster headaches. A review of the literature, including Jefferson's many letters, suggests that they probably were migraines, although not all of the current diagnostic criteria can be met.