Extremely low birth weight (ELBW) infants with periventricular leukomalacia (PVL) were examined by neuropathological and immunohistochemical methods. Thirteen ELBW infants of 85 infants with PVL, born at 23 to 27 weeks of gestation, showed a widespread type of distribution of PVL from the deep to intermediate white matter. Immunohistochemistry demonstrated glial fibrillary acidic protein (GFAP)-positive astrocytes to be increased in the deep white matter, often spreading to the intermediate white matter, in all cases of PVL. Tumor necrosis factor-alpha (TNF-alpha)-positive cells were found in the deep to intermediate white matter in 69% of PVL cases and appeared earlier, from 23 weeks of gestation, than in controls. beta-Amyloid precursor protein (beta APP)-positive axons were found around PVL in the deep to intermediate white matter in 85% of the cases. In age-matched control ELBW infants, GFAP-, TNF-alpha-, or beta APP-positive cells were never found. Therefore, in ELBW infants, widespread axonal damage and glial activation with cytokine production occur in the progression in characteristic PVL lesions.