Summary: The subject of the paper is the robust control of a class of sampled-data nonlinear systems with real time-varying parameter uncertainty and unknown cone-bounded nonlinearity. We consider the problems of robust stabilization and robust performance in an \(H_ \infty\) sense, and attention is focused on the design of linear dynamic sampled-data output feedback controllers. A control design methodology is proposed for solving both problems by recasting them into ‘scaled’ \(H_ \infty\) control problems for a related system which involve neither parameter uncertainty nor unknown nonlinearity.