In this paper, the problem of fault detection in sampled-data systems is studied. It is shown that norms of a sampled system are equal to the corresponding norms of a certain discrete time system. Based on this discretization, the sampled-data fault detection problem can be converted to an equivalent discrete-time problem. A framework that unifies the H-2 and optimal residual generators in sampled-data systems is then proposed. (c) 2005 Elsevier Ltd. All rights reserved.