Two brothers with hypohidrotic ectodermal dysplasia were found to have urticaria pigmentosa-like skin pigmentation with increased mast cells and melanin depositions in the dermis. Structural ciliary abnormalities of the respiratory tract were seen, and these may contribute to their severe recurrent chest infections. Primary hypothyroidism occurred in both by 3 years of age and responded to replacement therapy. The abnormalities seen appear to be the result of a common genetic aberration causing a particular sequence of maldevelopments during embryogenesis. This form of hypohidrotic ectodermal dysplasia associated with hypothyroidism gives a unique insight into the potential extent of structural defects of ectodermal dysplasias.