The amyloid fibrils of beta-amyloid (A beta) peptides play important roles in the pathology of Alzheimer's disease. Comprehensive solid-state NMR (SSNMR) structural studies on uniformly isotope-labeled A beta assemblies have been hampered for a long time by sample heterogeneity and low spectral resolution. In this work, SSNMR studies on well-ordered fibril samples of A beta(40) with an additional N-terminal methionine provide high-resolution spectra which lead to an accurate structural model. The fibrils studied here carry distinct structural features compared to previous reports. The inter-beta-strand contacts within the U-shaped beta-strand-turn-beta-strand motif are shifted, the N-terminal region adopts a beta-conformation, and new inter-monomer contacts occur at the protofilament interface. The revealed structural diversity in A beta fibrils points to a complex picture of A beta fibrillation.