CME ArticlePigmented Lesions of the Nail UnitNevares-Pomales, Oscar W. MD*; Sarriera-Lazaro, Carlos J. MD†; Barrera-Llaurador, Julian MD†; Santiago-Vazquez, Marely BS‡; Lugo-Fagundo, Nahyr BS§; Sanchez, Julio E. MD¶; Sanchez, Jorge L. MD¶Author Information *Resident in Dermatology (PGY4), Department of Dermatology, University of Puerto Rico Medical Sciences Campus, San Juan, Puerto Rico; †Physician, San Juan, Puerto Rico; ‡Medical Student (MS4), School of Medicine, University of Puerto Rico Medical Sciences Campus, San Juan, Puerto Rico; §Medical Student (MS3), Ponce Health Sciences University, Ponce, Puerto Rico; and ¶Faculty in Dermatopathology, Department of Dermatology, University of Puerto Rico Medical Sciences Campus, San Juan, Puerto Rico. Correspondence: Oscar W. Nevares, MD, School of Medicine, University of Puerto Rico, Medical Sciences Campus, P.O. Box 365067, San Juan, Puerto Rico 00936-5067 (e-mail: email@example.com). All authors and staff in a position to control the content of this CME activity and their spouses/life partners (if any) have disclosed that they have no financial relationships with, or financial interests in, any commercial organizations pertaining to this educational activity. The American Journal of Dermatopathology: November 2018 - Volume 40 - Issue 11 - p 793-804 doi: 10.1097/DAD.0000000000001106 Buy Metrics Abstract Pigmented lesions of the nail unit are commonly encountered in the clinical setting. Yet, they often present a unique challenge to clinicians because of a broad differential diagnosis or unfamiliarity with clinical and histopathologic features. A wide variety of causes exist ranging from benign lesions such as subungual hemorrhage to malignant lesions such as subungual melanoma. Identifying the underlying cause is key to appropriate management and follow-up in these patients. Although emerging clinical tools such as dermoscopy can be very useful in evaluation of these lesions, histopathologic analysis remains the gold standard. In this review, we discuss and provide a summary of important clinical and histopathological concepts of pigmented lesions of the nail unit with special focus on longitudinal melanonychia, melanotic macule, melanocytic nevus, subungual melanoma, along with discussion of some nonmelanocytic lesions. Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.