This review in the New England Journal of Medicine summarises recent progress in the understanding of the molecular and immunologic basis of psoriasis. The following topics are covered:

• Epidemiologic features and clinicopathological correlations

• Genetic factors

• Immunopathologic features of psoriasis

• Psoriatic microvasculature

• Models of psoriasis

• Psoriasis as a systemic inflammatory disease

• Pathogenesis-based approaches to therapy