The possibility that injury may play a role in the development of some forms of chronic inflammatory rheumatic disease has been a subject of debate for many years. Such a role is accepted for some cases of rheumatoid arthritis, remains controversial for spondylarthropathies, and is poorly understood in psoriatic arthritis. Three cases of post-traumatic psoriatic arthritis are reported herein. The difficulty of establishing the causative role of the injury (despite precise criteria) is underlined, the pathophysiologic mechanism is discussed (deep Koebner phenomenon?), and possible legal consequences are reviewed.