Pelvic organ prolapse (POP) is a process in which the pelvic contents, including the reproductive organ, bladder, rectum, and/or small intestines become herniated through defects in the vaginal wall. The pelvic organs are closely related to the urinary tract and thus various urinary functions can be affected. The purpose of this study was to evaluate the relationship between pelvic organ prolapse and lower urinary tract function by urodynamic studies. From March 1999 to May 2000, 40 patients with pelvic organ prolapse who underwent urodynamic studies (uroflowmetry, filling cystometry, urethral pressure profile) without barrier reduction of prolapse were analyzed. The majority of the cases of low grade POP involved patients with anterior wall prolapse, whereas the higher POP stages were more frequent in women with cervical cuff prolapse. Symptoms of stress urinary incontinence and hesitancy were more frequent in the patients with anterior wall prolapse. The urodynamic study showed a statistically significant increase in MUCP in patients with POP stage IV and the leading point of POP was cervical cuff. The subjective urinary symptoms of patients with POP appear to be less reliable as a diagnostic tool. POP had no adverse effect on the bladder storage function. However, POP affected the voiding function through an increase in MUCP, especially in patients with stage IV prolapse and when the leading point of POP was cervical cuff. Following the surgical correction of POP, an evaluation of the preoperative changes in the urodynamic study parameters should be performed.