A case of strumal carcinoid of the ovary is reported. The follicles contained T4-immunoreactive substance, whereas the carcinoid component of the tumor had a trabecular structure and showed argyrophilic elements. Pancreatic-polypeptide and enteroglucagon were localized in these cells by an immunocytochemical method. The same cells displayed small electron-dense endocrine-like granules. A common precursor for the thyroid and carcinoid components is postulated.