The dark watery vaginal discharge is due to the presence of melanoma in the vagina. Vaginal melanomas are thought to arise from melanocytes in the vaginal mucosa, which evolve from embryonic neural crest cells and can be found in the vaginal mucosa of 3% of adult women. Melanocytes get lost in the vaginal mucosa during their migration from the neural crest to the epidermis, and these ectopic melanocytes later become the source of vaginal melanoma development. Vaginal melanoma should be carefully differentiated from other rare melanin-containing tumors such as pigmented neurofibromas, and malignant neurocysticercosis. Vaginal melanomas are characterized by a variety of cell types, especially unpigmented vaginal melanomas that are easily misdiagnosed with squamous vaginal carcinomas, vaginal adenocarcinomas, and sarcomas, with a misdiagnosis rate of up to 20%. It is mainly differentiated from other diseases with the help of immunohistochemical staining and electron microscopic observation, which is more accurate than HMB-45 staining. It should also be thought to differentiate from the rare vaginal mucosal nevus of melanoma and to exclude metastases from other sites and invasion of malignant melanoma from neighboring organs, and changes in the mucosal junction are the most reliable basis for proving the primary.