OBJECTIVE To evaluate the prevalence of detrusor underactivity (DU) and bladder outlet obstruction (BOO) in women with high-grade cystocele and the impacts of cystocele repair. METHODS Between November 2010 and September 2018, women with ≥stage II cystocele were included. DU (detrusor pressure at maximum flow rate (PdetQmax) < 20 cmH2O, maximum flow rate (Qmax) < 15 mL/s, and bladder voiding efficiency < 90%) and BOO (PdetQmax ≥ 40 cmH2O and Qmax < 12 mL/s) were diagnosed by urodynamic study (UDS). Women who underwent cystocele repair were further analyzed with preoperative and postoperative comparisons. RESULTS A total of 623 women were included. Forty-four (7%) and 17 (3%) women were diagnosed with DU and BOO, respectively. Among the 314 operatively treated women, a significant increase in DU (7% vs. 15%, p = 0.0007), especially in those with stage III cystocele, and a slightly decreased rate of BOO were noted postoperatively. UDS revealed that the postvoid residual volume, functional profile length, maximum urethral closure pressure (MUCP), and pressure transmission ratio at the MUCP decreased significantly, as did the pad weight. Nearly all lower urinary tract symptoms (LUTS) improved significantly, except nocturnal enuresis. Among bladder diary parameters, nocturia episodes, daytime frequency, urgency episodes, and incontinence episodes decreased significantly after the operation. CONCLUSIONS The prevalence rates of DU and BOO in women with high-grade cystocele were 7% and 3%, respectively. After cystocele repair, the rate of DU increased. Most LUTS improved subjectively on questionnaires and objectively on UDS and bladder diary parameters after operation.