Abstract. The incidence of deep vein thrombosis (DVT), diagnosed by ascending phlebography, has been calculated retrospectively in a group of 14 869 obstetrical patients. The incidence was calculated to 0.13 per thousand antepartum and 0.61 per thousand postpartum. The study revealed that clinical signs and symptoms of thrombosis are very unreliable in pregnant women but more reliable in puerperal women. It is concluded that objective diagnosis of thrombosis is important in pregnant women, and ascending phlebography is a rewarding objective method to use in pregnant women.