The majority of ovarian sex cord tumors with annular tubules (SCTAT) are benign neoplasms that arise sporadically. In patients who have Peutz-Jeghers syndrome (PJS), ovarian SCTAT is often an incidental finding. Malignant behavior in SCTAT has heretofore been reported only in sporadic cases. We report a case of bilateral, malignant SCTAT developing in a 47-year-old woman who had PJS, originally diagnosed as adenocarcinoma on cervicovaginal cytology. Cervicovaginal and peritoneal fluid cytologic preparations were characterized by pseudopapillary clusters and three-dimensional tubes of tumor cells with scanty cytoplasm and high nuclear: cytoplasmic ratio. Examination of surgical resection specimens revealed bilateral, solid ovarian tumors composed of simple and complex annular tubules with hyaline cores, typical of SCTAT. Tumor emboli were present within salpingeal lymphovascular spaces and in both right and left pelvic lymph nodes. Flow cytometry of tumor cells demonstrated a diploid phenotype. This case represents the first documented example of bilateral, malignant SCTAT arising in a patient who had PJS, presenting with an atypical cervicovaginal smear.