In most cases the etiology of the focal ischemic stroke in newborns is still obscure. We considered patients with congenital hemiparesis due to a lesion in the territory of the middle cerebral artery (shown by CT or MRI) as a model of this infarction. A detailed history including maternal and familiar data was obtained from 9 affected patients. Duplex-sonography was performed and biochemical parameters were analysed in all patients and their mothers. There were no convincing hints for a prenatal (for instance infectious, traumatic or toxic) origin. Also the reconstruction of the perinatal period could not explain the infarction. Duplex-sonography revealed no anatomic variants of the intra- or extracerebral arteries. Haemostasiological results were within normal limits--except the antiphospholipid antibodies, which were detected in 7 of the 9 families (patient or mother). The significance of these results is still unknown. We propose, antiphospholipid antibodies and further haemostasiological parameters should be investigated as near as possible to the neonatal period.