Objectives: To assess 3 cm size threshold for follow-up of simple cysts in postmenopausal women.Materials and methods: Radiology information system was retrospectively queried for “US pelvis complete” over 8 years in women > 50 years, with keywords ovarian cyst, adnexal cyst, ovarian mass, cystic mass, cystic neoplasm, ovarian neoplasm, and ovarian mass. Premenopausal women were excluded. Cysts, were classified as ≤ 1 cm, 1–3 cm, 3–5 cm, and ≥ 7 cm. Largest cysts on each ovary was recorded. EMR and imaging archives were reviewed for assessing size, stability duration, and surgical records. Descriptive statistics and confidence interval were performed.Results: 4388 patients met the initial search criteria. 919 cysts in 896 women (age: 50–91 years, mean: 61.5 years) were identified. We found 162 cysts ≤ 1 cm, 352 1–3 cm, 296 3–7 cm , and 51 ≥ 7 cm cysts. 127 patients with 1–3 cm cysts had no follow-up. Final analysis of 225 1–3 cm cysts included 203 ovarian and 22 paraovarian cysts (average size = 1.95 cm (1.1–3.0 cm)). 103 ovarian cysts had less than 2 years, and 100 cysts had more than 2 years follow-up. All except one ovarian cyst were stable for the entire duration of their follow-up (Mean duration of follow-up 5.4 years) (0.3%, 95% CI 0.0–0.05). 40 cysts resolved. One simple cyst increased in size (followed over 3.25 years) without suspicious imaging features and benign on surgery.Conclusion: 1–3 cm cysts represented the most common size range (> 40%) in postmenopausal women, majority of which are stable over follow-up with benign outcome. 3 cm size threshold is appropriate for simple cyst follow-up in postmenopausal women.