A case of sialuria is described in a girl who presented in the neonatal period with hepatosplenomegaly, and who has moderate developmental delay at the age of 2 years. There was massive urinary excretion of free sialic acid (N-acetylneuraminic acid). The clinical, biochemical and ultramicroscopical features were distinct from those described in Salla disease and in infantile sialic acid storage disorder.