To assess the agreement between manual auscultatory arterial blood pressure values and the values obtained by an automated oscillometric device in normotensive pregnant patients. Arterial blood pressure was determined concomitantly by a Dinamap 1846 sx/p device and by one observer (I, IV, V Korotkoff sounds) blinded to the Dinamap values. Agreement between methods was tested and graded according to the protocol of the British Hypertension Society. A total of 490 observations were performed. Differences were observed between the manual auscultatory method and the Dinamap method. In monitoring normotensive pregnant patients with a Dinamap device, an error was made of about 10 mmHg in 22% of the observations for systolic arterial blood pressure (BP); in 11% for diastolic arterial BP (IV sound); and in 15% for diastolic arterial BP (V sound). According to the British Hypertension Society protocol, the overall grade reached was 'C'. Although an underestimation of only 10 mmHg was shown, this can be of great importance in delaying a correct diagnosis of pre-eclampsia. The assessment of agreement of the Dinamap 1846 sx/p device in hypertensive pregnant patients should also be determined. A prospective study could be useful to determine the effectiveness of an automated device in detecting hypertensive disease in pregnancy.