Introduction The aim of this study was to compare the posterior fornix syndrome (PFS), (abnormal bladder emptying, urge, frequency, nocturia, chronic pelvic pain) cured/improved by uterosacral ligament (USL) ligation, with ‘underactive bladder’ (UAB) , whose cause and cure of UAB are said to be unknown . Material and methods A limited literature search was carried out for the words posterior fornix syndrome; obstructed micturition; post-void residual. Results We found the diagnostic criteria used for UAB to be identical with PFS. Also, individual symptoms could be improved in the short term with squatting-based pelvic floor exercises, native tissue cardinal/uterosacral ligament repair, but requiring posterior ligament slings for a long term cure. Conclusions Because the similarity in symptoms may not be sufficient in the first instance to recommend surgery for UAB, we advise the use of a roll gauze or large tampon placed in the posterior fornix to support USLs ('simulated operation'), always with a full bladder, then observe any changes in PFS symptoms such as urge, pain, urine flow and post-void residual as a screening test before proceeding to surgery.