Sialidosis is a rare autosomal-recessive lysosomal storage disease due to mutations in the NEU1 gene leading to a deficit of alpha-n-acetyl neuraminidase and causing aberrant accumulation of sialylated glycoproteins/peptides and oligosaccharides in the lysosomes of various organs and tissues. Type II sialidosis (dysmorphic form) is classified into three subgroups based on the age of onset and the clinical severity: Congenital or neonatal, infantile (onset 0-12 months) and juvenile form (onset 13 months-20 years). We report the case of a 3-year-old boy with sialidosis type II infantile form, who developed a voluminous ascites. To the best of our knowledge, ascites is not described in the infantile form but in the congenital form of the disease. Ascites seems to be of a multifactorial origin regarding our investigations: on the one hand, portal hypertension and on the other hypoalbuminemia maintained by proteinuria secondary to nephrosialidosis. Loss of plasma proteins in the gastrointestinal tract (protein-losing enteropathy) should also be considered in the case of portal hypertension and damages of the reticuloendothelial system.