Arterial and venous structures in the deep white matter of the developing brain were examined by postmortem angiography. About the anterior horn, body and trigon of the lateral ventricle, ventriculopetal arteries reached the deep white matter and branched out to form an abundant network of small arterioles (hypervascular zone) particularly in premature brain, thus indicating the tentative border zone between ventriculofugal and petal arteries not to be hypovascular. A deep draining group of medullary veins converged at different zones in the deep white matter, becoming large to form a large converging zone, and finally drained into a subependymal vein. A fan-shaped draining area of the converging group of veins corresponded well to the area of periventricular leukomalacia (PVL) with the edema and hemorrhage. About the occipital horn and inferior horn of the lateral ventricle, transcerebral veins were abundant and PVL was rarely seen. The pathogenesis of PVL could not be fully explained by border zone infarct. An alternative pathogenesis of PVL is considered the following: 1) circulatory disturbance of the deep draining group of veins occurs, 2) edema with or without venous hemorrhage follows, 3) edema fluid and hemorrhage compress abundant arterioles in the deep white matter with 4) consequent coagulation necrosis.