Nonbacterial thrombotic endocarditis (NBTE) commonly occurs in advanced malignancies associated with a cancer-related hypercoagulable state, but the prevalence of NBTE in patients with less advanced malignancies is unknown. A 46-year-old woman had multiple thromboembolic events and disseminated intravascular coagulation on admission. Transthoracic echocardiography showed several growths on the mitral valve. Pelvic magnetic resonance imaging revealed a rapidly enlarging large tumor. In spite of anticoagulation therapy, she died 1.5 months after admission. At autopsy, NBTE with stage Ia ovarian cancer was diagnosed. In cases of higher-growth rate tumors with abundant necrosis, NBTE may occur in early-stage (even in stage Ia) ovarian cancer. In the majority of stage Ia ovarian cancers, curative surgical resection can be done. Prognostic improvement may be gained by such positive intervention, although this depends on the patient's general condition when NBTE occurs. With tumor resection, there is a possibility that the patient will recover from the hypercoagulable state and a poor outcome will be avoided.