The Buschke-Ollendorff syndrome is an association of cutaneous lesions, dermatofibrosis lenticularis disseminata, with osteopoikilosis. This condition is inherited in an autosomal dominant pattern. In order to clarify the biochemical nature of the skin lesions, we have examined 12 patients with the Buschke-Ollendorf syndrome, representing 2 unrelated kindreds. Histologically, the lesions were characterized by excessive amounts of unusually broad, interlacing elastic fibers in the dermis. Digestion of skin secretions with pancreatic elastase completely removed these fibers. Electron microscopy of the dermis further revealed markedly branched elastic fibers without fragmentation. The accumulation of elastin in the skin was also demonstrated by measurements of desmosine employing a radioimmunoassay. The desmosine content of the skin lesions increased 3- to 7-fold when compared to the skin either from healthy controls or from uninvolved skin adjacent to a lesion. The results indicate that the skin lesions of the Buschke-Ollendorff syndrome are connective tissue nevi of the elastin type. Cell cultures from these patients may provide a convenient model to study the control mechanisms involved in elastin metabolism.