Aims: The purpose of this study was to determine urodynamic features in hypospadic patients. Methods: Thirty-seven patients with hypospadias (distal: 31, proximal: 6) underwent preoperative urodynamic study according to International Continence Society (ICS) recommendations. Statistical analysis were done for comparison between urethral obstruction and non-obstruction in patients with detrusor overactivity (DO) plus the relationship of DO with localization of hipospadias. Results: Nearly 45.9% of the patients showed overactive detrusor. Urethral obstruction was found in 60.8% of the patients. The rate of DO was higher in proximal hipospadias, and urethral obstruction than distal type, and non-obstructed patients (P > 0.005). The means overall cystometric capacity, maximum voiding detrusor pressure and maximal urinary flow measured were 132.6 +/- 111.14 ml (range 21-610), 72 +/- 53 cmH(2)O (range 12-181), and 7.9 +/- 7.1 ml/sec (range 2-30 ml/sec), respectively. Conclusions: To the best of our knowledge, this is the first study ever to show that overactive detrusor is an accompanying entity in the hypospadic patients. (C) 2004 Wiley-Liss, Inc.