TDP-43 can form pathological proteinaceous aggregates linked to ALS and FTLD. Within the putative aggregation domain, engineered repeats of residues 341−366 can recruit endogenous TDP-43 into aggregates inside cells; however, the nature of these aggregates is a debatable issue. Recently, we showed that a coil to β-hairpin transition in a short peptide corresponding to TDP-43 residues 341−357 enables oligomerization. Here we provide definitive structural evidence for amyloid formation upon extensive characterization of TDP-43(341−357) via chromophore and antibody binding, electron microscopy (EM), solid-state NMR, and X-ray diffraction. On the basis of these findings, structural models for TDP-43(341−357) oligomers were constructed, refined, verified, and analyzed using docking, molecular dynamics, and semiempirical quantum mechanics methods. Interestingly, TDP-43(341−357) β-hairpins assemble into a novel parallel β-turn configuration showing cross-β spine, cooperative H-bonding, and tight side-chain packing. These results expand the amyloid foldome and could guide the development of future therapeutics to prevent this structural conversion. TDP-43 (transactive response DNA binding protein 43 kDa) is a protein implicated in RNA regulation. 1 Its binding to nucleic acids takes place through two RNA recognition motifs (RRM) located at the N-terminus, where sequences for nuclear localization and export are also present. TDP-43 is also associated with neurodegenerative diseases, as aggregates of this protein have been found in patients with amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration 2