Bladder instability and the nonneurogenic neurogenic bladder are 2 urodynamically different dysfunctional voiding patterns. However, they share a common urodynamic mechanism in that they both produce functional urinary obstruction, which by changing the anatomy and function of the bladder, and ureterovesical junction produces and perpetuates vesicoureteral reflux. Urodynamic studies show that bladder decompensation with high end filling pressures, rather than high voiding pressures, is the mechanism for reflux and help to explain the seemingly paradoxical relationship among obstruction, reflux and high bladder pressures, namely that reflux does not usually occur when bladder pressures are high. This urodynamic analysis and review of the literature strongly support the belief that functional urinary tract obstruction caused by dysfunctional voiding can initiate and perpetuate vesicoureteral reflux, and provide an understanding of the mechanisms involved.