Twelve cases of idiopathic thrombocytopenic purpura with a total of 42 pregnancies have been studied. During pregnancy both a clinical as well as a laboratory deterioration in the thrombocytopenia was observed in 8 patients. The course of thrombocytopenia varies in different pregnancies of the same patient, as illustrated in the reported case. Thrombocytopenia seems to affect fertility, 33% of pregnancies being terminated by spontaneous abortion. There was no increased rate of ante-partum or post-partum hemorrhage in this series. Toxemia of pregnancy does not seem to be related to thrombocytopenia, but steroid therapy may aggravate pre-existing toxemia. Vaginal delivery with minimal laceration of soft tissue is the method of choice. Idiopathic thrombocytopenia of the mother may affect the newborn. There was a 10.5% corrected fetal mortality due to thrombocytopenia. Seven newborns had a transient reduced thrombocyte count lasting some weeks. In 1 case persistent congenital thrombocytopenia was observed.