The ultrasonographic study through the fontanelle of 192 children below 33 weeks of age and surviving after the neonatal period led to the diagnosis of leukomalacia by identifying anechogenic cavities in the periventricular area in 7 cases. Clinical pictures were not characteristic. Important electro-encephalographic changes were constantly found, even before the occurrence of sonographic signs. Although non specific they are still suggestive when associated hemorrhage is not present. With these criteria, diagnosis seems to be correlated with severe neurologic prognosis. Its interest and chronology warrant the extension of the ultrasonographic supervision of severely immature infants up to the end of the second month.