To estimate the percentage of improvement in prolapse and urinary symptoms and adverse effects in women with advanced pelvic organ prolapse (POP) after 3 months of use of a ring pessary with support. In this prospective study, 109 consecutive women with advanced POP were fitted with a ring pessary with support; 73 (73/109, 67.0%) of the women had a successful 3-month pessary fitting trial. Prolapse symptoms, urinary symptoms, and urinary flow parameters were assessed at baseline and at 3 months. Adverse effects were assessed within 3 months. McNemar's test and paired-sample t tests were performed. Prolapse and urinary symptoms improved from baseline to 3 months, including bulging (90.4% to 23.3%; P <.001) and pressure (64.4% to 13.7%; P <.001). Voiding difficulty improved in 97.8% of the women (45/46; P <.001), splinting improved in 100% (19/19; P <.001), urge urinary incontinence improved in 76.9% (30/39; P <.001), and stress urinary incontinence improved in 58.1% (18/31; P = .025) after 3 months. After pessary treatment, the differences in maximum flow rate, mean flow rate, void volume, and postvoid residual at baseline and 3 months were statistically significant (P <.05). Vaginal discharge (32/73, 43.8%) was the most common adverse event. Vaginal ulcers developed in 7 (7/73, 9.6%) of the women. The ring pessary with support was successfully fitted in patients with advanced POP with a high success rate and few complications. The pessary could resolve more than half of the prolapse and urinary symptoms. Therefore, initial conservative treatment with a ring pessary with support in advanced POP is worthwhile.