The purposes of this study are (1) to describe a "late-onset" form of cystic periventricular leukomalacia eventually appearing in premature infants whose neurological assessments were normal in the first month of life; (2) to retrospectively evaluate its incidence among a large population of premature infants; (3) to suggest that a few unexpected complications of prematurity may trigger the development of white matter damage, even several weeks after birth. Retrospective study in a population of 1452 surviving infants after 5 days born before 33 weeks. We identified 10 cases of late-onset cystic periventricular leukomalacia appearing beyond the first 5 weeks of life. In 8 cases, an intercurrent event associated with a systemic inflammatory response preceded the appearance of cysts: necrotizing enterocolitis (n = 5), septicemia (n = 2 cases), strangulated inguinal hernia in one infant. Neurological surveillance should be repeated until discharge in very preterm infants, especially after the occurrence of an intercurrent complication coming along with a systemic inflammatory response.