In this report on a young female patient with hyalinosis cutis et mucosae (Urbach-Wiethe disease, lipoid proteinosis), we present the clinical, immunological and ultrastructural features of this inherited disorder and discuss the differential diagnosis against other interstitial connective tissue depositions. Immunologically, the most important result was the increased amount of collagen type IV at the junction zones of epidermis, dermal vessels and appendages. This was in accordance with the ultrastructural deposition of hyalin material, mainly consisting of multiplied basal laminae at the respective junction zones. The pathogenesis (gene defect or defective gene regulation?) and therapy are discussed.