OBJECTIVE To report two cases of prenatal Niemann-Pick disease type C in siblings, with different prenatal semiology and postnatal outcome. METHODS First fetus presented at 22 weeks'gestation with ascites, hepatosplenomegaly, then polyhydramnios. At birth, the infant developed severe cholestasis and died at day 5. His brother presented at 22 weeks'gestation an isolated hepatomegaly with cholestasis at birth showing favourable evolution. In first case, diagnosis of Niemann-Pick disease was confirmed by autopsy findings, biochemical tests on cultured skin fibroblasts and ascites fluid, then by molecular screening of NPC1 gene. Brother's molecular prenatal diagnosis was made at 14 weeks' gestation on cultured trophoblasts. CONCLUSIONS Prenatal screening of this disease is particularly indicated in case of fetal ascites with hypoferritinaemia. Tests on amniotic or ascites fluid cells allow to characterize the biochemical phenotype, leading to search for molecular abnormalities. Despite the same mutation identified in siblings, disease evolution is variable, which underlines complexity of genetic counselling.