OBJECTIVE: To compare the size of the genital hiatus in women wearing a pessary for pelvic organ prolapse after consistent pessary use, describe characteristics of patients who continue use, and assess change in pelvic floor symptoms. METHODS: This was an observational cohort study of 90 women seeking nonsurgical management of symptomatic prolapse. Our primary outcome was change in genital hiatus (in centimeters) after 3 months of consistent pessary use. Pelvic floor symptoms were assessed with the Pelvic Floor Distress Inventory. Change in genital hiatus measurements and Pelvic Floor Distress Inventory scores were assessed using a paired Student t test. Between-group differences were evaluated using the Student t, Mann Whitney U, and Fisher exact tests, where appropriate. Logistic regression was used to assess baseline characteristics predictive of continued pessary use. RESULTS: The average (±standard deviation) age of participants enrolled was 62.8 ±13.2 years. Median parity was 3, and 87.7% were postmenopausal. Forty-two (47%) continued pessary use at 3 months. After 2 weeks, there was a decrease in the size of the genital hiatus measured with strain from 4.8±1.6 cm to 4.1±1.2 cm, P<.001, which persisted at 3 months (3.9±1.1 cm, P<.001). The greatest change occurred with the Gellhorn pessary. Baseline Pelvic Organ Prolapse Quantification system point Aa was positively associated with continued pessary use at 3 months, and perineal body at rest was negatively associated. CONCLUSION: After 3 months of pessary use, genital hiatus size decreased significantly. Pessary use results in significant anatomic changes to the genital hiatus in patients with pelvic organ prolapse.