Abstract. In this note we show that the number of isomorphism classes of complemented subspaces of a reflexive Orlicz function space LΦ[0,1] is un- countable, as soon as LΦ[0,1] is not isomorphic to L2[0,1]. Also, we prove that the set of all separable Banach spaces that are isomorphic to such an LΦ[0,1] is analytic non-Borel. Moreover, by using the Boyd interpolation the- orem we extend some results on Lp [0, 1] spaces to the rearrangement invariant function spaces under natural conditions on their Boyd indices.