Myeloid sarcoma is a tumor of myoblasts or immature myeloid cells occurring in an extramedullary site. Myeloid sarcoma of the female genital tract as an isolated initial presentation or isolated relapse is very rare as evidenced from a literature review. We report a case of vulvar myeloid sarcoma presenting as isolated relapse of acute myeloid leukemia (AML) after allogeneic hematopoietic stem cell transplant (HSCT). A 41-year-old female diagnosed with AML M5 achieved remission with chemotherapy and underwent allogeneic HSCT from an HLA-matched sibling donor. The post-transplant period was complicated with chronic graft-versus-host disease. At 10 months post-transplant, she presented with a vulvar mass of six weeks duration. Excisional biopsy of the vulvar mass confirmed the diagnosis of myeloid sarcoma as extramedullary relapse. Bone marrow biopsy was without evidence of leukemia. Involvement of the vulva, vaginal and adjacent cervical area only was confirmed. She received re-induction chemotherapy with clinical regression of both the vulvar, vaginal and the cervical masses; this was followed by radiation therapy to an extramedullary site. The correct diagnosis of myeloid sarcoma, particularly of an isolated mass in the genital area, is important because of its rarity and the need for appropriate institution of therapy.