OBJECTIVE To further elucidate the mechanisms of overactive bladder coexisting with pelvic organ prolapse. METHODS A total of 100 consecutive women with stage 2 or greater pelvic organ prolapse associated with cystocele were enrolled in the present prospective study. They underwent urodynamic studies and then received tension-free vaginal mesh operation. Urodynamic studies were carried out before and after the correction of pelvic organ prolapse using a single gauze pack in the vagina in the sitting position. The overactive bladder symptom score and International Prostate Symptom Score were collected before and 3 months after surgery. RESULTS In 53 of 100 cases, pelvic organ prolapse was accompanied with overactive bladder, and detrusor overactivity was observed in 28 out of 53 pelvic organ prolapse with overactive bladder cases (52.8%). Detrusor overactivity was resolved in 18 and reduced in four out of 28 cases after the correction of pelvic organ prolapse by the gauze packing method. Of 53 patients who had overactive bladder preoperatively, overactive bladder symptoms disappeared in 35 cases (66.0%) and improved in six additional cases (11.3%) after tension-free vaginal mesh operation. A total of 20 of 25 cases whose overactive bladder symptoms disappeared or improved after surgery coincided with those who had shown either disappearance (n = 16) or improvement (n = 4) of detrusor overactivity after intravaginal gauze pack insertion in preoperative urodynamic studies. All scores in the overactive bladder symptom score decreased significantly after tension-free vaginal mesh, as well as the International Prostate Symptom Score, except for night-time frequency. CONCLUSIONS Pelvic organ prolapse-associated overactive bladder or detrusor overactivity conditions can be reversed in most cases within a short period of time after surgical correction of pelvic organ prolapse.