A new procedure is described for the synthesis of glycosyl cyanides by reaction of 1-O-acyl sugars with trimethyl-silyl cyanide in a polar aprotic solvent and in the presence of a Lewis acid as catalyst. A variety of ribosyl and arabinosyl cyanides have been made in this way from sugar derivatives having acyl, chloro, or methoxy leaving groups at the anomeric position, furanose or pyranose rings, and acyl or benzyl protecting groups. The 1,2-Trans-glycosyl cyanide was formed when the starting sugar had a participating 2-O-acyl substituent. A mixture of cyanide anomers was obtained when the starting sugar was protected with non-participating benzyl groups.