Treatment of moderate to severe Psoriasis (Pso) and Psoriasis-Arthritis (PsA) in Switzerland is largely performed with systemic therapies. This includes conventional systemic therapy such as fumaric acids, methotrexate, cyclosporin A, retinoids, systemic PUVA, Acitretin and biological treatments such as etanercept, infliximab, adalimumab and within a pre-registration program ustekinumab. While short- and middle-term efficacy of most systemic treatments has been shown in clinical studies (and is incorporated in international guidelines), knowledge about long-term outcomes, optimal treatment and effectiveness under real-world conditions is still missing. SDNTT, the Swiss registry on the treatment of moderate to severe Pso and PsA documents the long-term course of patients being administered a defined biologic or conventional systemic drug. Following outcomes are observed: Effectiveness on the long-term, of combined/alternating treatments and under comorbidity conditions; patient-defined benefits and quality of life, maintenance dosages, prediction of response and safety.