Let n be at least 5 and let W be a compact (n + 1)-dimensional h-cobordism between M and N in the category C=Diff, PL, or Top such that W, M and N are simply connected, then W is C-isomorphic to M × [0, 1].
This means that the homotopy equivalence between M, W, and N is homotopic to a C-isomorphism.