In metabolic diseases with fetal presentation, lysosomal storage disorders represent a fairly homogeneous group. Hydrops fetalis or ascites is the main but non specific symptom. The relative frequency of lysosomal storage diseases in this context is not well known and probably underestimated. They represent 1.4% in a large retrospective series. The contribution of the placental and fetal examination in their diagnosis is emphasized. The biological investigations required for their accurate pre and postnatal diagnosis are described. The precise identification of the lysosomal defect is necessary to propose an early prenatal diagnosis by chorionic villi biopsy in further pregnancies.