Preoperative water cystometrograms obtained from 437 patients with benign prostatic hyperplasia (BPH) were examined in a retrospective study. The cystometrographic results were analyzed regarding the preoperative clinical features: the patients' age, presence or absence of urinary incontinence, history of urinary retention, and rate of residual urine. Their prognostic value in terms of improvement in voiding difficulty and postoperative urinary incontinence was also analyzed at 1 and 6 months after elective transurethral resection of the prostate (TURP). Of these patients, 263 (60.2%) had detrusor instability (group I), whereas 174 did not (group II). Vesical denervation supersensitivity (Vds) to bethanecol chloride was noted in 47 (12.5%) of 375 patients. The observed difference in clinical features was significant between the two groups, with group I being older (P < 0.01) and showing a greater incidence of urinary incontinence (P < 0.001) and retention (P < 0.001). The difference seen between groups I and II in terms of mean bladder capacity (P < 0.01), compliance (P < 0.01), and a greater positive rate of Vds (P < 0.001) was also significant. The clinical and cystometrographic parameters studied worsened with advancing age of the patients. Although the majority of the patients (94.7%) were relieved of obstructive symptoms after TURP (6 months later), 113 (25.9%) showed no relief at 1 month.(ABSTRACT TRUNCATED AT 250 WORDS)