An adult case of mucolipidosis with beta-galactosidase and neuraminidase deficiencies is reported. The patient was a 35-year-old Japanese female with coarse face, lumbar vertebral beaking, action myoclonus, cerebellar ataxia, clouding of the cornea, macular cherry-red spots, hearing loss and vacuolated lymphocytes, but without mucopolysacchariduria. Her clinical symptoms developed at a late age with a slow progression. The enzyme activities of beta-galactosidase were deficient in leukocytes and cultured skin fibroblasts but normal in serum. Sialic acid-rich glycopeptides and oligosaccharides were increased in the urine. Neuraminidase activities toward fetuin, alpha-N-acetylneuraminosyl-(2 leads to 3) lactose and alpha-N-acetylneuraminosyl-(2 leads to 6) lactose were deficient in cultured fibroblasts. It is suggested that the main disturbance in the present case might be the catabolic process of glycoproteins and oligosaccharides due to neuraminidase deficiency.