SummaryFive cases of human listeriosis are presented, with a review of the 13 Belgian observations which have been published previously. These 18 cases show the clinical polymorphism of this illness and they can be divided into three important groups : the meningo-encephalitic (8) and septicaemic forms (1) in adults, the septicaemic (4) and pseudo-influenzal forms (2) in pregnant women, the meningitic (2) and septicaemic forms (1) in infants. This clinical study is completed with epidemiological, bacteriological, therapeutic and prognostic views. The high mortality of the fetal and meningo-encephalitic forms, and the necessity of a multivalent and massive antibiotherapy are stressed.