The goals of this study were to assess the efficacy of inside-out transobturator vaginal tape (TVT-O) as a treatment of urodynamic stress incontinence (USI) and to explore the possible factors determining surgical success and failure. Each woman had a 20-min pad test and urodynamic study including uroflowmetry, cystometry, and stress urethral pressure profile before and after treatment. Forty-six of the 54 women (85%) were cured of the disease, and two (4%) showed clinical improvement; TVT-O had failed to treat USI in six patients (11%) during the 9-month follow-up period. We assessed the relationship between clinical features, urodynamic parameters, and treatment outcome. Of these, only age and previous anti-incontinence surgery were significant risk factors for surgical failure. The success rate during the 9-month follow-up period decreased significantly in women > or =60 years and in women with previous anti-incontinence surgery. Women with USI can be treated by the TVT-O procedure.