The asymmetric introduction of the phenylselanyl moiety using chiral N-phenyselanylacetyloxazolidin-2-thiones and -thiazolidin-2-thiones is reported. The diastereoselectivity is complete in favor of the syn isomer and the aldols so obtained are valuable intermediates for the synthesis of more functionalized molecules such as amino alcohols, after chemoselective activation of the selenium and substitution by nucleophilic nitrogen.