Lipoid proteinosis is a rare autosomal recessive disorder with a chronic, benign course. There is no generally accepted systemic therapy apart from the experimental oral use of dimethyl sulphoxide (DMSO) and etretinate in two single cases. We treated two sisters and an unrelated man with lipoid proteinosis with longterm oral DMSO (60 mg/kg/d). At the end of an average treatment time of 3 years, DMSO was withdrawn because it produced no beneficial effects with regard to their skin, mucosal lesions or hoarseness. Additionally, one patient showed progression of her disease with worsening hoarseness and onset of dyspnea, requiring surgical removal of vocal cord infiltrates. Three patients with lipoid proteinosis failed to show any beneficial response to long term treatment with DMSO.