Struma ovarii is a rare tumor of the ovary pathologically resembling teratomas with thyroid components. The presenting clinical, radiological, and pathological features of patie-nts with consequent struma ovarii is diverse and does not give substantial information with regard to the nature of the ovarian tumor. Ten cases collected over a period of eight years from two institutes are presented which showed a wide diversity of clinical features, and in which the diagnosis was only made later by strict pathological criteria. The treatment for struma ovarii, and in even rarer cases, malignant struma ovarii, remains highly controvers-ial, but it is suggested that conservative treatment by tumor excision only may be sufficie-nt. Surgical treatment also greatly ameliorates any accompanying hydrothorax and ascites.