BACKGROUND: Nonbacterial thrombotic endocarditis (NBTE), or marantic endocarditis, is a rare form of endocarditis found in patients with advanced malignancy and collagen-vascular disorders. There is limited information about the clinical course of patients with NBTE because the majority of cases are found at the time of autopsy. CASE: A 38-year-old woman presented to the emergency department with recent onset of chest pain and fatigue. Initial evaluation revealed cardiac valvular disease, and the patient underwent aortic valve replacement. Final pathology revealed nonbacterial thrombotic endocarditis. A metastatic work-up revealed a complex pelvic mass and elevated CA 125. The patient underwent an exploratory laparotomy and was subsequently found to have synchronous primary endometrial and ovarian carcinoma. CONCLUSION: Nonbacterial thrombotic endocarditis is rare and carries a high mortality. This case is unusual in that the diagnosis of nonbacterial thrombotic endocarditis led to the diagnosis of a gynecologic malignancy. © 2006 by The American College of Obstetricians and Gynecologists. Published by Lippincott Williams & Wilkins.