Psoriatic arthritis is a comorbidity frequently associated to psoriasis. A major problem is the absence of diagnostic criteria and the lack of consensus on the classification criteria of this arthritis. The clinical presentation is extremely variable, since axial, peripheric, and enthesopathic lesions can exist alone, successively or in association in a same patient. Peripheric lesions can be mono- or more often oligo- or polyarthritis. Onychopathies and dactylitis are frequently associated to arthritis. The dermatologist must recognize psoriatic arthritis at an early stage, in order to avoid the development of destructive lesions. The treatment includes symptomatic treatments (antalgics, non steroidal anti-inflammatory agents, corticosteroids), long-term treatments (sulfasalazine, methotrexate, azathioprine, ciclosporine, leflunomide), and TNF-alpha-inhibitors. Therapeutic strategies must be adapted to the clinical presentation.