Aims: To describe the changes in urodynamic parameters and to assess patients' perceptions of voiding difficulties and improvements in symptom bother after solifenacin treatment in men with overactive bladder (OAB) and detrusor underactivity (DUA)., Methods: In this prospective study, 49 neurologically intact men were enrolled. DUA was defined as a bladder contractility index (BCI) <100. All subjects received 5 mg of solifenacin once a day for 120 days. A complete urodynamic study was carried out on the day before to the first dose of solifenacin and at day 120., Results: Solifenacin treatment resulted in a decrease in Q(max) during UDS (-0.6 ml/sec; P = 0.007), P(det)Q(max) (-6.4 cmH(2)O; P < 0.001), BOOI (-7.5; P < 0.001), BCI (-3.8; P = 0.001), BVE (-4.4%; P = 0.006), and voided volume (-7.5 ml; P = 0.09). On the contrary, PVR (+6 ml; P = 0.152), and maximum cystometric capacity (+22.9 ml; P = 0.001) increased. The regression analysis suggested that changes in urodynamic parameters after solifenacin treatment were limited for BOOI (9.4%), P(det)Q(max) (8.4%), and BCI (6.5%), with no significant impact on Q(max) during UDS, BVE, volume voided and PVR. No significant change in subjective perception of voiding difficulties was found. The incidence of AUR was 2.2% and improvement in patient's experience of OAB symptoms bother after solifenacin treatment was observed., Conclusions: Solifenacin treatment results in changes of urodynamic parameters. These changes, however, seem not to be of clinical significance as suggested by the lack of subjective deterioration in voiding difficulties and by the low incidence of AUR., ((c) 2008 Wiley-Liss, Inc.)