The goal of this study was to evaluate to what extent pregnancy influences headache recurrence in women with · diagnosis of migraine at, or before, their first prenatal visit. Data from the large, prospective Collaborative Perinatal Project of 55,000 pregnancies were reviewed. Less than 2% of women in the sample of first study pregnancies were considered to have migraine at their initial prenatal visit (n=508). Of the 484 women with a complete data set, 17% experienced complete cessation of headache throughout pregnancy and another 62% experienced two or fewer headaches in the third trimester. These observations lead to the conclusion that many migraineurs (79% in this sample) experience improvement in headache recurrence during pregnancy. Only 21% experienced no improvement at all. No demographic or obstetrical factor was associated with headache improvement.