Psoriatic arthritis (PsA), an inflammatory musculoskeletal disease associated with psoriasis, is a complex disease in terms of its clinical presentation, etiology, and pathogenesis. Musculoskeletal presentations include peripheral arthritis, spondylitis, enthesitis, and dactylitis. To learn about the course of and prognosis for such a complex disease, it is important to observe patients longitudinally so that all aspects of the disease are recognized. Several registries have been developed to evaluate the course of and prognosis for patients with PsA. Based on such registries, it has been shown that PsA is more severe than previously thought, and that progression of joint damage is related to joint inflammation. Such registries also have been used to determine genetic factors in PsA and to identify biomarkers for both susceptibility and expression of the disease. Drug registries also have been developed to document response to new therapies as well as the long-term adverse effects resulting from such therapies. It is hoped that an international effort currently on the way will further enhance the contribution of PsA patient registries to address the etiology, pathogenesis, and outcome of this complex disease.