We present a case of Hunter syndrome diagnosed because of skin eruption. A 4-year-old Japanese boy presented with a 3-4-months history of papular lesions on the back and extremities. His growth and development were almost normal. His face was not of coarse appearance. He had multiple, whitish to skin-coloured, papules and nodules symmetrically distributed on the scapular regions and the extensor aspects of the upper arms and thighs. There was no family history of similar symptoms. Skin biopsy showed the deposition of a considerable amount of mucin in the dermis. Although physical examinations failed to detect any other signs of Hunter syndrome, X-rays showed the characteristics features of mucopolysaccharidosis: deformities of the vertebral bone, ribs, and pelvis. Mucopolysaccharide analysis of the urine revealed a marked increase in dermatan sulphate and heparan sulphate. The activity of iduronate sulphatase in the lymphocytes was deficient, which was diagnostic for Hunter syndrome. We emphasize that the skin eruption can be the earliest sign of Hunter syndrome, particularly in the mild form presenting with normal development and growth.