An ultrastructural examination was carried out on the skin of six children suffering from Mucopolysaccharidosis I (MPSI or Hurler's disease) and MPS II (Hunter's disease). Both intracellular mucopolysaccharides and lipids were observed. The dermal cells, i.e. fibroblasts, macrophages, were loaded with multiple vacuolar inclusions thought to be of lysosomal origin. They appeared either content-free or filled with granular, fuzzy and/or pseudomyelinic structures. Identical abnormalities were observed within the Schwann cells, smooth muscle cells and keratinocytes. Mast cells showed peculiar "worm-like" inclusions apart from their normal granulations. Since ultrastructure of a skin sample may provide as much data as brain, liver or kidney, cutaneous electron microscopy can be recommended to confirm a diagnosis of MPS.