This study aims to examine the hypothesis that psychological factors may contribute to the aetiology of migraine, in that (i) specific personality traits may serve as predisposing factors, (ii) stressful emotional experiences may serve as precipitating factors. Epidemiological methods were used to obtain a random sample, in order to avoid the bias which may result from study of selected groups. Indeed, evidence was obtained in this study, that patients presenting themselves for treatment at special Migraine Clinics are not fully representative of migraine sufferers in general. From a survey of 1895 members of the Civil Service, comprising a wide range of ages, and all social strata, a random sample of 50 men and 50 women migraine subjects were taken. These were matched for control purposes with similar groups who suffered non-migraine headaches, and groups who were not affected by headaches. Further matched groups were also studied; these were, 18 women Migraine Clinic patients, to ascertain whether their characteristics were similar to those of unselected migraine subjects; and 19 asthmatic male Civil Servants, to ascertain whether they as sufferers from a different psychosomatic disorder, displayed similar personality characteristics to the migraine subjects. Two hundred and thirty seven individuals were interviewed in order to obtain details of personal history, medical history, and family history. Three psychometric tests: (1) the Eysenck Personality Inventory, (2) an abridged form of the Minnesota Multiphasic Personality Inventory, (3) the Buss Durkee Hostility/Guilt Inventory were completed by each participant. The following main items were found to be correlated at statistically significant levels with the occurrence of migraine. (1) Increase in ‘N’ scores of EPI (and this was confirmed in an additional 166 Migraine Clinic patients). (2) Increase in anxiety and somatisation scores on MMPI (women only). (3) Increase in hostility scores on Buss Scale. (4) Evidence of increased emotionality, in that migraine sufferers had significantly more psychological symptoms than controls. No objective evidence of greater past or present emotional stress was found in migraine subjects as compared with controls. It is suggested that these findings are evidence for increase reactivity of the automatic nervous system in migraine subjects and that this may provide a predisposing factor for the development of migraine attacks. Evidence is also presented that emotional stress can act as a precipitating factor in migraine, since over one half of 120 attacks recorded during a two month period of observation, were related in time to an overtly stressful event; and in half of the random sample, migraine began for the first time ever, during a period of emotional stress.