Bernard-Soulier syndrome (BSS) is a congenital autosomal recessive bleeding disorder characterised by giant platelets, the lack of thrombocytopenia or a moderate one, prolongation of skin bleeding time, and absent platelet aggregation in response to ristocetin. We report a case of BSS revealed by major neonatal thrombocytopenia. A newborn was admitted for thrombocytopenic purpura initially believed to be due to a maternal auto-immune thrombocytopenia. Because of the persistence of the thrombopenia till the age of 7 months despite therapy by corticosteroids and immunoglobulins, and because of the detection of anti-1b antiplatelets antibodies after transfusion, BSS diagnosis was evoked. In such a situation of major thrombocytopenia, the main therapeutic measure is prevention. Therapy by DDAVP may be used after the age of 3 years in situations of high haemorrhagic risk. This case report underlines the importance of a precise diagnosis in front of a maternal thrombocytopenia and the possibility of antenatal diagnosis of BSS.