Psoriatic arthritis is an inflammatory arthropathy associated with psoriasis and is classified as a seronegative spondyloarthropathy. It occurs in approximately 5% to 7% of patients with psoriasis. The etiopathogenesis of psoriatic arthritis is not well known, but interaction among genetic, immunologic, and environmental factors is believed to play a key role in the development and clinical expression of the disease. Studies on intercellular interactions, particularly concerning the role of cytokines, growth factors, and intercellular adhesion molecules, have provided new insights into the pathogenesis. A new clinical classification has been introduced based on the experience of a British group. New concepts in the topography (chest, lower limbs, temporomandibular joint) and extra-articular manifestations of the disease have been reported. The usefulness of the erythrocyte sedimentation rate and of bone scintigraphy in the evaluation and follow-up of patients with psoriatic arthritis has also been reported.