(dimethylsilyl)acetonitriles (Me2HSiCR3R4CN) react spontaneously with aldehydes in DMSO to give β-hydroxynitriles in good to high yields. The addition to ketones is effectively promoted by using MgCl2 or CaCl2. (Dimethylsilyl)acetonitrile (Me2HSiCH2CN) shows lower reactivity than the α-alkylated analogues. However, the parent reagent adds efficiently to aldehydes and ketones under catalysis by AcOLi or MgCl2.