The development of the microvascular architecture of the cerebral cortex and white matter was studied in the preterm, term, and older infant, using postmortem cerebral angiography and metal impregnation studies. During the first few months after birth, a relatively avascular triangle forms in the white matter at the depth of the sulcus. Subcortical leukomalacia occurs in this triangle as well as in border zones between the major cerebral arteries.