Prurigo pigmentosa is unique among inflammatory diseases of the skin. More than 200 patients with prurigo pigmentosa have been reported on in Japan, but as of today fewer than 40 non-Japanese patients have come to notice. In order to establish reliable, repeatable criteria for diagnosis of prurigo pigmentosa, we studied more than 70 patients with the disease, most of them Japanese, and reviewed the entire international literature devoted to the subject.