To compare the quality of life and clinical findings of patients with low-pressure urethra (LPU: < or = 20 cm H2O) with those of stress urinary incontinent (SUI) patients without LPU, and to compare the quality of urethral sphincter (US) muscle innervation parameters in LPU patients with those in control continent patients. Historical, clinical, urodynamic, and US muscle innervation parameters were compared in 38 LPU (group 1), 241 SUI (group 2), and 7 control patients (group 3). In comparison with group 2, the incidence of previous surgery and daily incontinence episodes, SUI severity, and pad test values were significantly higher in group 1, whereas the incidence of previous traumatic deliveries was the same in both groups. The mobility of the bladder neck assessed by the Q-Tip test was significantly reduced in group 1. In comparison with group 3, US motor unit potential (MUP) duration and pudendal motor latencies to the urethral sphincter (PMLUS) were increased in LPU group 1 patients, whereas there was no difference in these parameters between LPU patients with or without previous incontinence surgery. Fifty-three percent of our LPU patients had normal PMLUS, but showed signs of abnormal reinnervation on quantitative electromyography. Three nullipara LPU patients had normal MUP durations and PMLUS values, but a decreased area in response to pudendal nerve stimulation. Apart from a rare form of LPU in nullipara patients, probably due to a dysgenesis of their US muscle, LPU patients suffer from neuro-muscular damage responsible for a severe urinary invalidity. Previous incontinence surgery, as well as previous vaginal deliveries, may be responsible for such US damage.