A 28-year-old woman with a previous history of recurrent benign ovarian teratoma developed a bilateral horizontal gaze palsy, a right facial paresis, and bilateral trigeminal hypesthesia. Magnetic resonance imaging disclosed high signal in the rostral pons. Results of all other laboratory studies, including those for antineuronal antibodies (anti-Hu, anti-Yo, anti-Ri, anti-Tr, anti-Ma1, anti-Ma2, and anti-CV2/CRMP5), were negative. Pelvic ultrasound revealed a residual mass in the left ovary, which was confirmed as teratoma on surgical pathological examination. Complete neurologic recovery occurred within two weeks of surgical removal of the teratoma and treatment with intravenous corticosteroids and immunoglobulin. This case demonstrates that a search for an occult neoplasm is extremely important in the diagnosis of presumed paraneoplastic encephalitis even if antineuronal antibodies are not found.