Psoriasis is a common chronic skin disorder estimated to affect about 2% of the Western population. The disease creates a significant stigma for patients and is a major economic burden. Psoriasis has a large spectrum of clinical features and evolution. Clinical features of chronic psoriasis are generally sufficient to make the diagnosis. Diagnostic doubts, however, may arise in several clinical variants and atypical cases or when the psoriatic lesions are localized in particular sites.