In this paper robust stability and performance conditions for the classical unity-feedback control system and for a more general feedback configuration are proposed. Uncertainty is represented in the linear fractional form, where perturbations are assumed to be norm-bounded, stable and unstructured. Suitable Hinf control problems are derived for satisfying both the proposed sufficient conditions. In addition, it is shown that the first condition puts in a unified framework some conditions existing in the literature and referring to specific kinds of perturbations, such as the additive and the multiplicative ones. Lastly, a property of the family of perturbed systems whose robust stabilization is guaranteed by the first condition is derived.