Report on a 30-year old primigravida with a family history of bleeding and a personal history of nasopharyngeal bleeding since age four. Severe menorrhagia since her menarche. First seen at 20 weeks gestation with naso-pharyngeal bleeding and a twin pregnancy. The patient was found to have Glanzmann's disease (congenital thrombasthenia) with an excessive lack of factor XIII. Ambulatory treatment with packed cell transfusions until 35 weeks gestation. The thrombelastogram did not improve with transfusions of platelet concentrates. In-patient treatment from 35 to 37 weeks gestation, no vaginal bleeding throughout the pregnancy. Elective Caesarean hysterectomy at 37 weeks gestation with lo units fresh blood, 3 units platelet concentrate and 10 ampules factor XIII concentrate in readiness. Delivery of twin girls 3180 and 3050 g without signs of Glanzmann's disease. Treatment of the maternal bleeding by replacement. Factor XIII 80% of normal 8 weeks postpartum. This appears to be the first case of twin pregnancy in the presence of Glanzmann's disease and the fourth case in the world literature.