Let G be a compact Lie group acting smoothly on a smooth, compact manifold M , let P ∈ ψ m (M ; E 0 , E 1 ) be a G-invariant, classical pseudodifferential operator acting between sections of two vector bundles E i → M , i = 0, 1, and let α be an irreducible representation of the group G. Then P induces a map πα(P ) : H s (M ; E 0 )α → H s−m (M ; E 1 )α between the α-isotypical components. We prove that the map πα(P ) is Fredholm if, and only if, P is transversally α-elliptic, a condition defined in terms of the principal symbol of P and the action of G on the vector bundles E i .