Abstract.Let C be an additive category such that idempotent endomorphisms have kernels, C a class of objects of C having Dedekind domains as endomorphism rings, and assume that if X and Y are quasi-isomorphic objects of C then Hom(X, Y") is a torsion-free module over the endomorphism ring of X. lîA®B = Ci®---®Cn with each C¿ in C, then A = A\ ©• ■ •©Am, where each Aj is locally in C, and End(A,) ~ End(C¿) for some i. The proof includes a characterization of tiled orders. Moreover, there is a "local" uniqueness for finite direct sums of objects of C.Let' C be an additive category such that idempotent endomorphisms of objects of C have kernels and let G be a class of objects of C with Dedekind domains as endomorphism rings. Two objects A and B of G are quasi-isomorphic if there are maps / G Hom(A, P) and g G Hom(P, A) with fg ?* 0. The class G has the torsionfree-hom condition if whenever A and B are quasi-isomorphic objects of G then Hom(A, B) is a torsion-free £'(A)-module, where E(A) is the endomorphism ring of A. If A and X are objects of C such that E(A) and E(X) are integral domains and if P is a prime ideal of E(A) then A is isomorphic to X at P if there are maps