Pityriasis rotunda is an uncommon dermatosis characterized by multiple, widely distributed, strikingly circular hypopigmented or hyperpigmented patches that are slightly scaly. It has been described in Oriental and black patients, usually in association with certain infective or malignant systemic diseases. Pityriasis rotunda is rare in white patients and does not act as a marker of malignancy. Our ultrastructural and histologic findings demonstrated that pityriasis rotunda is more closely related to congenital ichthyoses than ichthyosis vulgaris, contrary to previous reports. On the basis of our studies and a review of the literature, it seems that two types of pityriasis rotunda exist with significant prognostic differences.