The second edition ofDifferential Diagnosis inDermatology I by A. Bernard Ackerman, with the assistance of two visiting fellows at New York (NY) University, is an update of the edition published more than 15 years ago, with new photographs. It is an atlas in which pairs of microscopically similar cutaneous diseases are compared. For each pair, a clinical photograph and three photomicrographs in color are shown side by side on a single page. The pictures are of generally good quality but are three inches or less in greatest dimension and, in some cases, details are hard to see even at the highest magnification shown. Thus, the pictures of simple lentigo do not showmelanocytic hyperplasia clearly and, despite the aid of lines drawn to show particular microscopic features, differences between a Spitz nevus and malignant melanoma