The development of carcinoma in a neovagina is a rare occurrence. A case of mucinous adenocarcinoma of a neovagina is presented. A neovagina was formed in 1945 to correct a congenital anomaly. Subsequently the patient developed a chronic rectovaginal fistula. It is thought that the mucinous adenocarcinoma developed as a result of chronic inflammation secondary to the fistula. Although rare, development of a malignancy in ectopic tissue can occur. Clinicians need to be aware of this as they follow these patients.