We report a new case of GM1-gangliosidosis diagnosed in a 5 months old baby who was admitted at birth to our Neonatology Unit because of congenital ascites. The antenatal diagnostic techniques, including ultrasound, maternal antibody screen and fetoscopy with fetal karyotyping, as well as postnatal exhaustive study, failed to determine the underlying cause. Because of progressive neurologic deterioration a lysosomal storage disease was suspected and confirmed by skin biopsy. We wish to add a new case of a lysosomal storage disease to the growing list of nonimmune hydrops fetalis etiologies, and to highlight the importance of enzymatic studies in chorionic villous sample or amniotic cultured cells, once the most common conditions associated with fetal ascitis have been ruled out.