Two patients with Darier's disease—diagnosed clinically by the presence of characteristic keratotic papules in seborrheic areas—were biopsied for light- and electron-microscopic studies. Light microscopy revealed typical histologic features of Darier's disease. Ultrastructural studies showed the presence of cytoplasmic processes projecting from the basal keratinocytes (basal keratino-cyte herniations) into the underyling dermis through small defects in the basal lamina, which was intact in some areas but in other locations showed thickening, irregularity, and replication. Widening of the lamina lucida with partial or complete disappearance of hemidesmo-somes were noted in many areas.