  We classify the possible discrete (finite) symmetries of two--dimensional
critical models described by unitary minimal conformally invariant theories. We
find that all but six models have the group Z_2 as maximal symmetry. Among the
six exceptional theories, four have no symmetry at all, while the other two are
the familiar critical and tricritical 3--Potts models, which both have an S_3
symmetry. These symmetries are the expected ones, and coincide with the
automorphism groups of the Dynkin diagrams of simply--laced simple Lie algebras
ADE. We note that extended chiral algebras, when present, are almost never
preserved in the frustrated sectors.
