The purpose of this study was to evaluate the presence of headache in women with a previous history or new-onset headache during the current gestation, classify the findings, and describe the clinical characteristics and outcome of the headache. From January/1998 to June/2002 we prospectively evaluated 1101 pregnant women (12-45 years old), with a history of headache, at two prenatal clinics and an inpatient obstetric public hospital. Women were interviewed using a semi-structured questionnaire during the first, second, and third gestation trimesters and immediately after delivery. All interviews were conducted by one of the authors, using the International Headache Society Classification (IHSC-2004). In 1029 women there was a history of headache prior to the current pregnancy, 36 (3.4%) women first experienced headache during this pregnancy and 40 patients experienced new types of headache. In these 76 patients with new onset headache during pregnancy, 40 had secondary headache (52.6%), 31 had primary headache (40.8%), and 5 had headache not classified elsewhere (6.6%). According to IHSC- 2004 criteria, we found migraine in 848/1029 women (82.4%), with pregestational headache. Most of the pregnant women presented with headache, mainly in migraine, prior to pregnancy, and most of the headaches improved or disappeared during the second and third gestation trimester. In a relatively small number of pregnant women, a new type of headache started during the gestation.34187-92