Objective: The purpose of this study was to evaluate the presence of headache in women with a previous history or newonset headache during the current gestation, classify the findings, and describe the clinical characteristics and outcome of the headache. Methods: 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 all 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). Results: 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. Conclusions: 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 In a relatively small number of pregnant women, a new type of headache started during the gestation.342187192