OBJECTIVE To determine if there is an association between migraines and intrapulmonary right-to-left shunt. BACKGROUND Several studies have described an association between migraines and intracardiac right-to-left shunt. METHODS Patients with hereditary hemorrhagic telangiectasia (HHT) were retrospectively recruited from the Toronto Hereditary Hemorrhagic Telangiectasia Center Clinical Database. All patients had been prospectively, systematically asked about a history of migraines and systematically screened for pulmonary and cerebral arteriovenous malformations (AVMs). All patients with a definite diagnosis of HHT, assessed during a 2-year period (February 1997 to April 1999), were included. Univariate analyses and logistic regression were performed, for migraine as the dependent variable and the following independent variables: age, sex, pulmonary AVMs, and cerebral AVMs. RESULTS Of the 200 patients assessed during the 2-year period, 124 (62%) had a definite diagnosis of HHT and were included in the analysis. Eighty (65%) were females. Forty-seven (38%) of the HHT patients had a history of migraine, of whom 38 (81%) had migraine with aura. The prevalence of migraine was greater in patients with pulmonary AVMs (46%) compared to patients without pulmonary AVMs (33%), OR = 1.7 (0.8 to 3.6), though this did not reach statistical significance (P = .14). Pulmonary AVMs were significantly associated with migraine (OR = 2.4, 95% CI = 1.1 to 5.5, P = .04), after adjustment for age and sex, using logistic regression. CONCLUSIONS There is a significant association between intrapulmonary right-to-left shunt and migraine.