There has been substantial research carried out on the errors in variables (EIV) identifiability problem for dynamic systems. These results are spread across a significant volume of literature. Here, we present a single theorem which compactly summarizes many of the known results. The theorem also covers several cases which we believe to be novel. We analyze single input single output systems using second order properties. We also extend the results to a class of multivariable systems. (C) 2007 Elsevier Ltd. All rights reserved.