Sialic acid storage disorder, known as Salla disease, is a rare autosomal recessive lysosomal disorder produced by a defect of a proton-driven carrier that is responsible for the efflux of sialic acid from the lysosomal compartment. We report two patients with Salla disease: a two-year-old girl, presented with hypotonia, inability to speak and walk, bilateral optic atrophies, defective myelination, cerebellar atrophy, and thinning of the corpus callosum on magnetic resonance imaging (MRI), who was classified as intermediate severe Salla disease; and a four-year-old girl, presented with relatively late-onset, slight hypotonia, and delayed language and mobility development, and supported by relatively protected MRI findings, who was classified as conventional Salla disease. Diagnosis of Salla disease was confirmed by accumulation of sialic acid in fibroblast culture: 15.1 and 13.2 nmol/mg protein in the first and second patient, respectively. Optic atrophy observed in the first case may be an additional feature besides the characteristic manifestations of Salla disease.