Ovarian stromal tumors range from fibroma to thecoma, depending on the degree of luteinization of tumor cells. They occur in peri- and postmenopausal women and are most commonly unilateral. The mitotic rate is the main feature helping predict the behavior of these tumors: while usual fibromas and thecomas are virtually amitotic, mitotic rate of 4 or more mitotic figures per 10 high-power fields is used as a cutoff to diagnose a fibrosarcoma. Fibrosarcomas, in addition to an increased mitotic rate, are also hypercellular and exhibit significant cytologic atypia; some may show tumor cell necrosis and could be adherent to adjacent pelvic organs, causing difficulty at surgery. Fibrosarcomas pursue a malignant clinical course, with local recurrence and metastases, usually to the lungs. Tumors with increased cellularity and mitotic counts of 3 or fewer mitoses per 10 high-power fields are termed cellular fibromas and have a somewhat increased likelihood of local recurrence after a long period of time, especially if they were adherent to pelvic organs or were ruptured at surgery. Ovarian stromal tumors may present a diagnostic difficulty when they undergo torsion with infarction and cystic change, which may render their histologic recognition problematic. Thorough sampling, along with immunohistochemistry for α-inhibin and calretinin, may help in making the correct diagnosis. Fibromas may be associated with several clinical and genetic syndromes, most notably Meigs syndrome, consisting of ascites and pleural effusions which resolve after tumor removal, and a hereditary Gorlin syndrome, consisting of multiple basal cell carcinomas, cysts of the jaw, and other neoplasms, including ovarian fibromas.