Abstract Objective: To detect temporal case clustering in patients with pityriasis rosea in different geographic locations. Design: Regression analysis of dates on which 1379 patients were diagnosed as having pityriasis rosea in 3 different geographic locations. The control data consisted of dates of diagnosis of patients with psoriasis in the same settings. Setting: Dermatology clinics in Kuwait, Minnesota, and Diyarbakir, Turkey.Patients Patients with pityriasis rosea and psoriasis seeking care in the clinics. Results: Three significant positive clusters (P = .005, P =.001, and P =.01, respectively) and 1 significant negative cluster (P<.001) were detected in these series of patients. No cluster was detected in 2 corresponding series of patients with psoriasis in Kuwait and Turkey. Conclusion: Temporal case clustering exists in pityriasis rosea. Comment in Enterovirus infection as a possible cause of pityriasis rosea: demonstration by immunochemical staining. Chia JK, Shitabata P, Wu J, Chia AY.Arch Dermatol. 2006 Jul;142(7):942-3. doi: 10.1001/archderm.142.7.942.PMID: 16847226 No abstract available.