Dark black urine, also known as dark brown urine, is most often seen in patients with melanoma. Melanoma produces too much melanin. In the liver small melanin is reduced to melanogen. If a large amount of melaninogen is excreted from the urine, it becomes melanin after oxidation of wren, so the urine of a melanoma patient, if left for a little while, becomes black urine. Prevention and treatment of dark black urine: Avoiding sunlight as much as possible and using shade screens are important primary prevention measures, especially for those at high risk, and it is more important to strengthen education for the general public and professionals to improve the three early, i.e. early detection, early diagnosis and early treatment. 1. For pigmented nevi occurring in areas prone to friction, biopsies should be taken for pathological examination. For example, children with large hairy nevi in the waist, which are often rubbed and squeezed by the belt, should have all of them removed as early as possible. If it is difficult to remove all of them at one time, the main part of the mole can be removed in the middle of the mole before malignant transformation, and the skin around the mole can be sutured on both sides, and then the rest of the mole can be removed until all of the mole is removed to prevent malignant transformation. Each specimen must be sent for pathological examination. If there is malignant change, all the specimens should be removed and implantation should be performed. 2. It is not advisable to stimulate the nevus with corrosive drugs or thorough freezing. It is dangerous to repeatedly freeze the nevus several times because it often becomes malignant due to traumatic stimulation. It has been reported that it was someone who had malignant changes due to incomplete freezing at one time. About 30% to 50% of malignant melanomas are related to external irritation. It is safer and more reliable to remove the mole at one time if it is needed for cosmetic reasons. The combination of freezing and excision should be strived to be completed at one time, and it is important not to excise it in parts, and the excised specimen should be sent for pathological examination.