Perinatal listeriosis is a disease whose incidence has increased constantly in recent years. Like neonatal infection determined by B hemolyticus streptococcus, the disease appears in two forms: the first is the septicaemic form with early onset, the second form is meningoencephalitic with late onset. We describe a case of listeriosis with immediate onset in which, in spite of the prompt therapy and the normality of rachiocentesis, developed a purulent ventriculitis with outcome in hydrocephalus.