Objective: To investigate the cognitive functioning of migraineurs vs nonmigra ineurs in a large population-based sample of middle-aged twins where headache diagnoses were established by neurologists. Methods: Twins identified through th e population-based Danish Twin Registry participated in face-to-face structur ed interviews, which included cognitive tests and two previously validated quest ions screening for migraine. Twins who screened positive for migraine and their co-twins were invited to participate in a telephone-based interview conducted by neurologists, who established headache diagnoses according to the Internation al Headache Society criteria. Cognitive scores on fluency, digit span, delayed w ord recall, and symbol digit substitution test were compared between migraineurs and nonmigraineurs. Comparisons within monozygotic and dizygotic same sex twin pairs discordant for migraine were also performed. Results: Of the 1,789 twins w ho were eligible forinclusion in the present study, 1,393 (77.8%) were intervie wed.A diagnosis of migraine was established in 536 twins (migraine without aura n = 347; migraine with aura n = 157). Average scores on cognitive tests in twins with migraine or one of the migraine subtypes did not differ from those of nonm igraineurs in any of the tests. Comparisons within twin pairs discordant for mig raine produced highly comparable results. Adjustment for possible confounders an d stratification by cumulated number of lifetime attacks did not influence the r esults. Conclusions: A lifetime diagnosis of migraine was not associated with co gnitive deficits in middle-aged subjects. Objective: To investigate the cognitive functioning of migraineurs vs nonmigra ineurs in a large population-based sample of middle-aged twins where headache diagnoses were established by neurologists. Methods: Twins identified through th e population-based Danish Twin Registry participated in face-to -face structur ed interviews, which included cognitive tests and two previously validated quest ions screening for migraine. their co-twins were invited to participate in a telephone-based interview conducted by neurologists, who established headache diagnoses according to the Internation al Headache Society criteria. Cognitive scores on fluency, digit span, delayed w ord recall, and symbol digit substitution test were compared between migraineurs and nonmigraineurs. Comparisons within monozygotic and dizygotic same sex twin pairs discordant for migraine were also performed. Results : Of the 1,789 twins w ho were eligible forinclusion in the prese nt study, 1,393 (77.8%) were intervie wed. A diagnosis of migraine was established in 536 twins (migraine without aura n = 347; migraine with aura n = 157). Average scores on cognitive tests in twins with migraine or one of the Adjustment for possible confounders an d stratification by cumulated number of lifetime attacks did not influence the r esults. Conclusions : A lifetime diagnosis of migraine was not associated with co gnitive deficits in middle-aged subjects.