The paper considers minimum-phase nonlinear systems that are subject to bounded parametric uncertainties. The parametric uncertainties are not required to enter linearly in the state equations. The problem addressed concerns the design of a nonlinear state feedback controller such that the closed-loop system is input to state stable (ISS) for any input belonging to L-infinity[0, infinity). Based on the normal form of a nonlinear minimum-phase system, a robust ISS controller is designed by applying the so-called ’backstepping’ technique. Furthermore, the L-2-gain from the input to the output of the closed-loop system is guaranteed to be less than or equal to a prespecified level for all admissible uncertainties.