Nail Matrix Nevi, a common cause of longitudinal black nail in children, is a pigmented nevus that occurs on the nail matrix. It produces melanin that advances with the nail plate to the nail edge, showing longitudinal brown-black streaks on the nail plate. Nail nevi can involve all fingers or toes, with fingers being more common, especially the thumbs. It may appear as one or more longitudinal pigmented bands extending from the proximal nail crease to the distal end and may range in color from light brown to black and in width from hairline to full nail width. The nail folds may be positive for Hutchinson’s sign (hyperpigmentation in the proximal nail fold or subcutaneous nail that semi-follows the longitudinal black nail; in adults, a positive sign is often indicative of a risk of malignant melanoma), and there may be hyperpigmentation of the perinail tissue. The nail nevus is not self-resolving, but the pigment produced may decrease. The choice of treatment is still debated because of the low incidence of melanoma in children and the fact that biopsy and excision of nail nevi can result in nail disfigurement. Because the incidence of nail malignant melanoma during childhood is extremely low, regular follow-up of longitudinal nail is generally safe, but because nail nevus can continue to widen with age and there are reports of malignant melanoma in situ in the nail matrix of children, our current opinion is that if the nail is gradually widening, early excision can be considered, the damage to the nail will be smaller and the nail disfigurement will be lighter.