The stability properties and design rules for a class of robust integrating regulators are considered. Passivity arguments are employed to define bounds on the parameters of an extended PID regulator and to establish the robustness of the closed-loop stability properties in the presence of sector-bounded non-linear elements in the feedback loop. This approach allows linear and non-linear single-input/single-output and multi-input/multi-oulput systems to be considered in the same framework.