A female patient of Italian, non-Jewish, descent, 22 years of age, with cloudy corneae, capsular lens opacities and severe and progressive mental and motor deterioration is described. Ultrastructural examination of a skin biopsy sample showed storage of membranous cytoplasmic bodies in Schwann cells, vessel walls, fibroblasts, smooth muscle fibres and sweat glands, and the presence of some electron-lucent vacuoles, filled with fibrillo-granular material, in sweat glands. Biochemical analysis of cultured fibroblasts (from skin explant) showed a complete deficiency of the sialidase acting on gangliosides, while the sialidase acting on sialyllactose and MU-NeuAc, and several lysomal hydrolases were normal. The urine sediment analysis showed accumulation of all phospholipid species, of several glycolipids and of gangliosides, especially of the polysialylated species. We conclude that the patient under examination is affected by Mucolipidosis IV and the term 'sialolipidosis' is suggested for this inborn disorder.