Searching for the term psoriasis in a major online bookstore revealed 1737 hits (November 12, 2003). These books covered all facets of psoriasis, from specialist-written textbooks to weltanschauung-driven guidebooks on self-help healing. Why, one might therefore ask, would this subject need a new edition of a book on the treatment of moderate to severe psoriasis? There are at least two good reasons. First, because the first edition has been a excellent treatment guide. And second, because there are probably only a few disorders other than psoriasis that recently have experienced such a dramatic change in their conceptual understanding and in the treatment approaches arising from these novel pathogenetic insights. Updating pathogenetic knowledge and integrating the new treatment approaches into the current therapeutic armamentarium are therefore fundamental challenges in dealing with psoriasis as a clinician.