INTRODUCTION: Several studies have reported that migraine headaches are more common in patients with allergic rhinitis and that immunotherapy decreases the frequency of headache in atopic headache sufferers. OBJECTIVE: To determine if the degree of allergic sensitization and the administration of immunotherapy are associated with the prevalence, frequency, and disability of migraine headache in patients with allergic rhinitis. METHODS: Consecutive patients between the ages of 18-65 presenting to an allergy practice that received a diagnosis of an allergic rhinitis subtype (eg, allergic or mixed rhinitis) were enrolled in this study. All participants underwent allergy testing as well as a structured verbal headache diagnostic interview to ascertain the clinical characteristics of each headache type. Those reporting headaches were later assigned a headache diagnosis by a headache specialist blinded to the rhinitis diagnosis based on 2004 International Classification Headache Disorders-2 (ICHD-2) diagnostic criteria. Migraine prevalence was defined as the percentage of patients with a diagnosis of migraine headache (ICHD-2 diagnoses 1.1-1.5). Migraine frequency represented the number of days per month with migraine headache self-reported during the headache interview and migraine disability was the number of days with disability obtained from the Migraine Disability Assessment questionnaire. Generalized linear models were used to analyze the migraine prevalence, frequency, and disability with the degree of allergic sensitization (percentage of positive allergy tests) and administration of immunotherapy as covariates. Patients were categorized into high (> 45% positive allergy tests) and low (/= 40 years of age. In subjects 45 years of age, there was no effect of degree of allergic sensitization or immunotherapy on the frequency and disability of migraine headache. CONCLUSIONS: Our study suggests that the association of allergy with migraine headaches depends upon age, degree of allergic sensitization, administration of immunotherapy, and the type of headache outcome measure that are studied. Lower "degrees of atopy" are associated with less frequent and disabling migraine headaches in younger subjects while higher degrees were associated with more frequent migraines. The administration of immunotherapy is associated with a decreased prevalence, frequency, and disability of migraine headache in younger subjects.