We examined the urodynamics, particularly voiding dysfunction, in patients with a neobladder. Free uroflowmetry, pressure-flow study, and voiding cystourethrography were performed in 22 patients (mean age 65 years) at a mean of 21 months after ileal neobladder substitution. The results of free uroflowmetry were used to divide patients into two groups: the good voiders and the poor. Daytime continence was achieved in all patients, while 10 (45%) had nighttime continence. To void 250 ml urine the good voiders strained 2 +/- 1.5 times, and the poor voiders 6 +/- 5 times. The neobladder neck was at the most caudal portion of the reservoir in good voiders, and there was wide funneling. In the group with poor emptying ability, the outlet was not located at the most dependent position. The principal factors for ensuring good voiding function in neobladder patients are the ability to perform effective straining and the location of the neobladder neck.