Variations of urethral pressure were registered with microtransducers in 427 gynecologic patients with lower urinary tract symptoms during urethrocystometry. Urethral instability (variation of urethral pressure greater than 15 cm of water) was found in 16.4% of patients. The comparison of the urinary symptoms and the urodynamic data between patients with urethral instability (without previous surgery for incontinence, N=57), and patients with stable urethra (variation of urethral pressure less than 5 cm of water, N=269) showed that urethral instability was related to frequency, nycturia, urgency, and a history of urethral syndrome. In 27% of patients, the urethral instability was associated with a bladder instability. The comparison between patients with urethral instability and stable bladder (N=51) and patients with bladder instability and stable urethra (N=41) revealed that bladder instability seems to be more important than urethral instability as a factor associated with nycturia, urgency, and urge incontinence.