Molecular dynamics simulation techniques have been used to investigate the effect of 2,2,2-trifluoroethanol (TFE) as a cosolvent on the stability of three different secondary structure-forming peptides: the alpha-helix from Melittin, the three-stranded beta-sheet peptide Betanova, and the beta-hairpin 41-56 from the B1 domain of protein G. The peptides were studied in pure water and 30% (vol/vol) TFE/water mixtures at 300 K. The simulations suggest that the stabilizing effect of TFE is induced by the preferential aggregation of TFE molecules around the peptides. This coating displaces water, thereby removing alternative hydrogen-bonding partners and providing a low dielectric environment that favors the formation of intrapeptide hydrogen bonds. Because TFE interacts only weakly with nonpolar residues, hydrophobic interactions within the peptides are not disrupted. As a consequence, TFE promotes stability rather than inducing denaturation.