A nail mother nevus is a pigmented nevus that grows on the nail mother cell. It is the same as pigmented nevus that grows on other parts of the body, except that the nail mother cell is the part of the body that synthesizes the nail, so nevus that grows on this part will appear as a black vertical stripe on the nail with a smooth surface and clear edges for a long time. As long as this kind of nevus does not change, such as widening, uneven pigmentation, etc., it usually does not need to be treated. We should be alert to whether it is symmetrical, whether the edges are irregularly arranged in a jagged shape, whether the color is all black or uneven, and whether the diameter is greater than 3mm, etc. These are all indicators that need to be observed, and if there is no tendency of malignant transformation, no treatment is needed, but patients should be advised to follow up regularly.