  In this paper we present a Friedmann-Robertson-Walker cosmological model
conformally coupled to a massive scalar field where the WKB approximation fails
to reproduce the exact solution to the Wheeler-DeWitt equation for large
Universes. The breakdown of the WKB approximation follows the same pattern than
in semiclassical physics of chaotic systems, and it is associated to the
development of small scale structure in the wave function. This result puts in
doubt the ``WKB interpretation'' of Quantum Cosmology.
