An abnormal life-threatening haemorrhagic diathesis occurred 6 weeks after delivery in a 25-year-old female. The reason was a spontaneously acquired factor VIIIC inhibitor haemophilia. The clinical presentation was characterised by extensive deep-seated soft-tissue haemorrhages of the extremities, a retroperitoneal haemorrhage, haematuria and recurrent joint bleedings. The activity of factor VIIIC decreased to below 1% of normal. The factor VIII inhibitor reached a maximum of 122 Bethesda units. The recurrent knee joint haemorrhages responded well to treatment with an activated prothrombin complex concentrate (Feiba). Repeated Feiba administration did not lead to an increase of the factor VIII inhibitor. It disappeared completely within 16 months and did not recur during a second pregnancy. The pregnancy was without complications and delivery on time resulted in a healthy child. Six months after the second pregnancy both mother and child showed no evidence of a disorder of haemostasis.