This note discusses a class of large-scale systems composed of symmetrically interconnected identical subsystems. We consider the decentralized H-infinity control design problem and study the fault tolerance of the resulting system. By exploiting the special structure of the systems, a sufficient condition for the existence of a decentralized H-infinity controller is derived. Moreover, for the nominal case as well as for contingent situations characterized by control channel failures, the poles and the H-infinity-norm of the closed-loop system can be calculated easily based on certain systems of reduced dimensions. Consequently, the tolerance to actuator failure can be easily tested.