The successful introduction of anti-tumor necrosis factor (TNF) therapies in psoriasis and psoriatic arthritis has sharpened considerable interest in this chronic and frequently disabling disease. Unlike the situation in rheumatoid arthritis, where anti-TNF therapies were introduced after years of painstaking research which confirmed a key proinflammatory role for TNF, the evidence for TNF having a key role in psoriatic arthritis has lagged behind. In this paper, the emerging immunohistochemical, genetic, and clinical literature relating to TNF's role in skin and joint manifestations of this disease is reviewed and areas for future research are suggested.