Peroxyacetals 2a–2j were prepared by TiCl4-promoted nucleophilic addition of both tert-butyl hydroperoxide (TBHP) and an alcohol to the corresponding aldehyde. The reaction works well with a variety of aldehydes, but not with ketones. The magnitude of the equilibrium constant for hemiacetal formation plays an important role; a large constant enables high conversion to peroxyacetal.