Book excerpt: Tis book originated as a small reference manual that I created to serve as an educational supplement for the dermatology residents a-t Loui siana State University Health Sciences Center. Deeming the compiled information to be useful for all dermatologists, I decided to expand the text and publish it. Every major category of the patient evaluation, from the chief complaint to the diagnosis, is addressed with regard to the dermatological diferential diagnosis. Te establishment of a precise diferential diagnosis for a gi- ven cu taneous problem is the fundamental challenge that the dermatologist faces with every patient. Tis unique exercise is very intellectual; in a short period of time the clinician must select from a list of perhaps several hundred diseases a few possibilities that match the clinic-al pre sentation. Tis is performed while also negotiating the patient - interac tion, examining the patient, and beginning to formulate a pla- n of ac tion. Profciency in the formulation of a diferential diagnosis that is brief and simultaneously thorough allows for consideration of- all pos sibilities, proper evaluation, and, hopefully, rapid diagnosis. We hope to provide the target readers (dermatologists and dermatologists- -in-train ing) with some assistance in carrying out this frequently complicated task. For the confrontation with an atypical presentation of a common disease or the classic presentation of an uncommon disease, the reader will hopefully fnd this book very useful.