A persistent interdigital dermatosis of the feet is occasionally observed, characterized by white hyperkeratotic thickening between the toes and over the adjoining area of the soles, which defies efforts to demonstrate fungous organisms and resists topical treatment almost absolutely. Regarding the condition as a distinctive entity, Castellani1 applied to it the name "pseudotinea interdigitalis pedum." The opportunity to study a number of cases of this intertriginous eruption has yielded the data presented in this paper. Examination of the morphologic aspects of the lesions, including their histopathologic structure, and search for concomitant involvement of other areas of the body have sustained my impression that the disease is an atypical form of psoriasis. Because the outstanding feature (and the one least likely to suggest psoriasis) is its white, sodden appearance, I have adopted the name "white psoriasis" as appropriately descriptive of the condition clinically. An alternative name, "hyperkeratotic psoriasis," indicates the