In this note we study the robustness of optimal organizational architectures, focusing on hierarchies and polyarchies. These two specific architectures are often applied in economic systems and have received considerable attention in the literature. It turns out that the application of these architectures usually involves inefficiency, namely, the use of suboptimal organizational systems. This is demonstrated by proposing a measure of size robustness of optimal architectures and by analyzing the implications of its magnitude for hierarchies and polyarchies. © Springer-Verlag 2001.