Psoriasis vulgaris, affecting the skin, is one of the most common organ-specific autoimmune diseases in humans. Until recently, psoriasis was treated by agents or approaches discovered largely through serendipity. Many of the available drugs were inherently quite toxic when used as continuous treatment for many years in this chronic disease. However, an increasing understanding of disease-specific immune pathways has spurred development of pathway-targeted therapeutics during the past decade. Psoriasis is now the most effectively treated human autoimmune disease, with high-level clinical improvements possible in ∼90% of patients using a new generation of drugs that selectively target the IL-23/Type 17 T cell axis. Thus, psoriasis is a model for the success of a translational-medicine approach based on cellular and molecular dissection of disease pathogenesis in humans.