Helicobacter cinaedi is a rarely encountered pathogen that easily induces bacteremia. Various foci of H. cinaedi infection have been reported; however, no case of adnexal abscess caused by H. cinaedi has been reported in the English literature. We herein report a case of ovarian abscess caused by H. cinaedi. A 38-year-old nulligravid Japanese woman was admitted to our hospital with an adnexal abscess. Clinical findings included fever, leukocytosis, and elevated C-reactive protein. Laparoscopic right partial oophorectomy with abdominal lavage was performed. H. cinaedi was isolated from cultures of blood and ovarian abscess fluid after surgery. Intravenous ampicillin/sulbactam was administered for 2 weeks, followed by oral amoxicillin for an additional 2 weeks. The postoperative course was uneventful and clinical findings improved. There was no evidence of relapse. H. cinaedi can cause ovarian abscess and is likely an under-recognized pathogen.