We conducted a survey by questionnaire to clarify the actual conditions of neonates born to mothers with autoimmune thrombocytopenic purpura (ATP) in Japan. We investigated 93 pregnancies (1 resulting in twins) in 31 hospitals between 1985 and 1994. Forty-nine of the neonates (52%) had thrombocytopenia (below 150 x 10(9)/L). Nineteen neonates (20%) showed a bleeding tendency, but this was generally mild. In only one neonate (1%) (a case of asymptomatic intracranial hemorrhage, ICH), deep bleeding occurred due to thrombocytopenia. The lowest platelet count of neonates after birth occurred on day 4, not on day 0. There was no correlation between maternal and neonatal platelet counts. However, there was an apparent correlation between the neonatal platelet count on day 0 and the lowest platelet count after birth. Treatment of the mothers with intravenous high-dose gamma-globulin and prednisolone did not prevent risk of neonatal thrombocytopenia significantly.