• chronic headache;
  • etiology;
  • onset;
  • injury;
  • pregnancy;
  • stress

In a data base of 1013 patients with chronic headache, 44.1% reported the onset of headaches before the age of 20 (preadult-onset headache) and 55.9% at or after that age (adult-onset headache). Circumstances of headache onset were mentioned significantly more frequently in the latter than in the former group (8.5% versus 38.2%, P<.001). The 10 most common circumstances of headache onset in adult-onset chronic headache, accounting for 87.9% of all circumstances mentioned, are further discussed. The 3 most common factors, accounting for 58.4% of all circumstances, were head, neck, or back injury; stress; and pregnancy. Illnesses, influenzalike and otherwise, and estrogen administration for birth control or hormone replacement shared the fourth place. It is concluded that in the etiology of chronic headache, other than genetic factors should be considered as well.