In 1972, Wolcott and Rallison described three siblings with a combination of infancy-onset diabetes mellitus and multiple epiphyseal dysplasia. We have observed a brother and sister with the same disorder. The chondro-osseous lesions are those of a spondylo-epiphyseal dysplasia. The diabetes mellitus is relatively mild. Histologic and electron microscopic studies of chondro-osseous tissue show findings similar to those in other epiphyseal and spondylo-epiphyseal dysplasias. In addition, however, atypical collagen-like fibres are found inside and outside chondrocytes. Collagen production seems to be normal in cultured fibroblasts. From the available data it appears that the association of characteristic chondro-osseous and endocrine abnormalities is non-random and that the lesions are independent manifestations of a pleiotropic gene. We propose to call this disorder the Wolcott-Rallison Syndrome.