The present knowledge on periventricular leucomalacia is reviewed. Its incidence is about 10% in preterms infants < 32 gestational weeks. By careful ultrasonographic scanning four stages can be distinguished: Prolonged flares, resolution, cystic leucomalacia, ventriculomegaly. Periventricular leucomalacia (PVL) is much more correlated with later neurologic impairment than intraventricular haemorrhage (apart from grade IV). PVL is caused by ischemia of the periventricular white matter mainly due to arterial hypotension and disturbed regulation of cerebral blood flow. The interactions between blood pressure, pCO2, pO2 and cerebral blood flow are complex and poorly understood. Regarding the clinical management it seems important to avoid hypotension, fluctuating pCO2 and hypoxemia/anemia in order to prevent white matter ischemia. Research should be focussed on the development of monitoring methods (doppler sonography, near infrared spectroscopy, time compressed electroencephalography), which allow to detect ischemic events to prevent neurologic impairment in about 1000 preterm infants per year in Germany.