Most headaches, including the chronic ones, have an organic background. This applies in particular to the unilateral headaches, but also probably to some of the global ones. In spite of this, there seems to be a clear, but variable influence of stress in the various types of headache. This effect may be a dual one. Thus, in migraine the effect of the low-degree, daily, annoying stress may be much worse than that of major stress, which may in fact prevent a headache almost even completely. A distinction should be made between the influence of stress on the headache as such and on the separate attacks. An example of this may be cluster headache: the mechanism underlying the long-term development may be under influences of external stressors, whereas the shortlasting, solitary attacks are scarcely influenced by such factors. The negative influence of stress is probably most apparent in common migraine and the acute form of tension headache. Headaches like the "atypical facial neuralgia" have been thought to have a strong, psychogenic background. Atypical facial neuralgia is one of the unilateral headaches, and bears a great similarity to cervicogenic headache. In the latter headache, attacks may even be precipitated mechanically, so that a psychogenesis or a marked stress-influence seems to be unlikely. In some cases of classic migraine, attacks seem to appear in their own inherent, stereotypical rhythm irrespective of outer events of a possible harmful nature.