The most important and most commonly occurring form of psoriasis is psoriasis vulgaris. In the specialism of rheumatology palmoplantar pustulosis is also important. The outcome is influenced mainly by how severe and how widespread the manifestations affecting the skin and nails are. All manifestations affecting the joints and occurring in association with psoriasis are subsumed under the term 'psoriatic arthritis' (PsA). Asymmetric oligoarthritis, enthesitis and inflammatory spinal manifestations are especially frequent. PsA is a rheumatic illness with widely varying clinical pictures, most patients having signs and symptoms resembling those of spondyloarthritides (SpA) and other features of rheumatoid arthritis (RA) and/or of arthrosis/osteoarthritis (OA). Clinical features that are particularly typical of PsA are ray-wise joint involvement, dactylitis and osteodestructive and osteoproliferative joint destruction. Dactylitis, asymmetric joint involvement and enthesitis also occur in other SpA. It is becoming increasingly important to define outcome parameters for use in PsA against the backdrop of new forms of treatment. In the case of clinical outcome basic distinctions must be made between clinical signs and symptoms, function and structure. In PsA the sometimes significant manifestations affecting skin and nails must also be considered. The outcome parameters used thus far have varied very widely. The extent and intensity of involvement of the peripheral joints and insertions of tendons and of spinal involvement are particularly important in PsA. In addition, functional impairments, quality of life and parameters concerned with work must be considered. There are hardly any measuring instruments specific to PsA; many have been developed and used primarily for SpA or RA.