Acquired perforating dermatosis (APD) is a skin disorder occurring in the patients with chronic renal failure (CRF), diabetes mellitus (DM) or both. The purpose of this study was to clarify the clinical and histopathological features of APD, and evaluate role of scratching in the pathogenesis of APD. Twelve patients with APD associated with CRF and DM were enrolled in the study. In six patients who required hemodialysis, the lesions appeared 2-5 yr (mean 3 yr) after the initiation of dialysis, 18-22 yr (mean 19.3 yr) after the occurrence of DM. The other patients who did not receive hemodialysis noted the lesions 4-17 yr (mean 9.5 yr) after the onset of DM. All patients had an eruption of generally pruritic keratotic papules and nodules, primarily on the extensor surface of the extremities and the trunk. The histologic features of our cases showed a crateriform invagination of the epidermis filled by a parakeratotic plug and basophilic cellular debris. The period of treatment for patients who suffered from severe (7 cases) or very severe (3 cases) on the pruritus intensity was longer than that of patients who had mild pruritus (2 cases). These data showed that scratching appear to play a critical part in the pathogenesis of APD.