In this paper an unselected series of 19 twins with migraine is reported. The findings in 13 pairs with ascertained twin diagnosis, 3 MZ and 10 DZ, are preliminarily summarized. With regard to typical migraine, only 1 MZ pair was concordant, a minor degree, of concordance was seen with all MZ and 3 DZ pairs. Regarding a distinct picture of vegetative dystonia, all MZ and 2 DZ pairs were concordant. On the basis of these results it can be assumed that various etiological factors are responsible for the manifestation of hemicrania. The hereditary basis seems to lie in a vegetative, diencephalic, dysregulation. Besides, the clinical manifestion is determinated by various preformative influences of an endogenous or exogenous nature.