Objective: To assess the potential for malignancy in ultrasonographic low-score persistent ovarian formations in postmenopausal women. Methods: In the Department of Gynecology of a University Hospital, an expectant management was offered to a cohort of 86 postmenopausal patients with unilocular persistent ovarian formations between 50 and 100 mm diameter. After informed consent, they were prospectively followed by means of transvaginal ultrasonography and CA 125 serum measurement annually for 9 years. Results: Of the 86 women, 41 (47.6%) had no changes in ovarian cyst diameter (mean diameter 69 mm, range 52 – 95) or CA 125 serum concentrations in the follow-up period. In 24 women (27.9%), the cyst disappeared between different follow-up visits. 21 patients (24.4%) underwent surgery for any reason and the ovaries were resected. No ovarian malignancy was diagnosed in any case in our series. Conclusion: Consistent with our hypothesis, follow up with transvaginal sonography and serum CA 125 measurement is not strictly necessary in postmenopausal patients with unilocular ovarian formations between 50 and 100 mm diameter.