For m greater than or equal to 5, we prove that a stationary extrinsic (or intrinsic) biharmonic map u is an element of W-2,W-2(Omega, N) from Omega subset of R-m into a Riemannian manifold N is smooth away from a closed set of (m - 4)-dimensional Hausdorff measure zero. (C) 2004 Wiley Periodicals, Inc.