We report a 39-year-old patient with a huge connective tissue naevus on his back, in association with pseudo-Hurler polydystrophy (mucolipidosis III). As far as we are aware, this is the first report of the coexistence of these two rare conditions. The lesional skin was composed of densely packed, coarse collagen fibres, which were immunohistochemically found to consist of type I, type III and type VI collagens. The amount of elastic fibres was moderately reduced. The glycosaminoglycan content of lesional skin was similar to that in a normal control. Activities of several glycosidases were markedly decreased in cultured fibroblasts.