BACKGROUND: Crohn's disease is a chronic inflammatory disorder characterized by focal, transmural inflammation of the intestine. Gynecologic involvement, including rectovaginal fistula formation, is frequent. Case #1. A 53-year-old female with a 30-year history of Crohn's disease and numerous perirectal fistulas developed a foul smelling, purulent drainage from her rectum and a mucopurulent, bloody discharge from her vagina. A lower vaginal lesion biopsy demonstrated a low-grade mucinous adenocarcinoma. Case #2. A 42-year-old female with a 15-year history of Crohn's disease developed drainage from her vagina. Physical examination revealed an enlarging mass involving the posterior wall of the vaginal vault that connected to the anus by a fistula tract. A biopsy revealed mucinous adenocarcinoma. CONCLUSIONS: Malignant transformation of persistent rectovaginal fistulas is a potential complication of Crohn's disease.