During the treatment of extracorporeal photopheresis (ECP), white blood cells are collected by apheresis and exposed to ultraviolet A after incubation with 8-methoxypsoralen. Although ECP was first developed for cutaneous T cell lymphoma, it has shown promising efficacy in a number of other serious conditions, like acute and chronic graft-versus-host disease, lung and cardiac transplant rejection and other autoimmune diseases. The ECP has been used for thirty years in some specialized centers but remains unknown to most of the physicians. The aim of this article is to review the practical aspects, the mode of action and the current indications of ECP.