Thrombotic thrombocytopenic purpura (TTP) is a hematologic disorder which is clinically characterized by thrombocytopenia, microangiopathic hemolytic anemia, fever, neurologic symptoms, and cardiac and renal involvement. The pathogenic mechanisms of this disease are poorly understood. It is well known that TTP is associated with pregnancy and that prognosis for the mother and child is poor. We present the first case of a severe TTP diagnosed in the first trimester of pregnancy (13th week of gestation) with maternal survival and birth of a healthy child which required continuous and intensive treatment with plasma therapy until delivery. During a period of 24 weeks several attempts to discontinue plasma therapy failed because of continuous active disease, and it became evident that plasma infusions were not as effective as plasma exchanges. The fact that the patient entered into remission soon after delivery of a healthy child by cesarean section in the 37th gestational week shows that in this case pregnancy activated an unknown factor which does not cross the placenta and which can be removed by plasmapheresis.