Pessary treatment for pelvic organ prolapse (POP) has a success rate of only 63% and its working mechanism remains unclear. This study applies upright MRI to gain insight into pessary. Patients were scanned in supine and upright position. The pessary was located under the inferior pubic bone in 7 out of 9 patients in upright position, opposed to 1 out of 9 in supine position. This indicates that the pubic bone does not (solely) contribute to the supporting mechanism. The use of upright MRI contributes to knowledge about the working mechanism of the pessary.