Alloimmunization of the mother against foetal alloantigens can cause neonatal alloimmune thrombocytopenia (NAITP). The recurrence rate is high (90%). The thrombocytopenia in subsequent children is often more severe. Most feared are intracranial haemorrhages (ICH). Current diagnostics indicate that ICH often occurs in utero or during labour. Postnatal therapy is therefore of limited value. We treated three women who had had earlier newborns with severe NAITP, in 5 subsequent pregnancies with weekly high dose intravenous IgG from week 30-34. Four newborns of two women had no thrombocytopenia at birth. Only in one child was the NAITP as severe as in the previous affected sibling. We conclude that antenatal therapy with weekly high dose intravenous IgG is safe and often effective. In utero transfusions are indicated only in exceptional cases.