We describe the neuropathologic and ultrasonographic findings in 22 very low birth weight infants (mean weight 948 gm) who survived at least 6 days and for whom cranial ultrasonography had been performed three or more times in life. White matter necrosis was found in 15 of the 22 subjects and was judged chronic (5 days' duration or longer) in seven subjects. The most common pattern was diffuse necrosis of hemispheric white matter, found in 10 of 15 infants; restriction of necrosis to the periventricular region was found in only three infants. The classic histologic features of periventricular leukomalacia were absent from 7 of the 15 infants with necrosis. Seventeen infants had intraventricular hemorrhage, but extension of ventricular blood into white matter unaffected by infarction was not found. Two ultrasonographic features were associated with white matter necrosis: increased parenchymal echogenicity and ventricular enlargement. One or both of these findings were present in 67% of infants with white matter necrosis, in 90% of infants with diffuse necrosis, but in no infant without necrosis. Increased parenchymal echogenicity was seen in all four infants with hemorrhagic necrosis, in 60% of infants with diffuse necrosis, but in none of the five infants with localized necrosis. We conclude that the very small infants now dying in nurseries have a form of white matter damage that is more extensive than, and in some cases histologically different from, periventricular leukomalacia as originally described. Ultrasonography as used in this study identified most but not all infants with pathologically verified white matter necrosis.