Abstract: Solid catalyst components comprising Ti,Mg, halogen and an internal electron-donor compound selected from the 1,3-diethers of formula (I) in which R is a C1-C10 alkyl group, R1 is a linear or branched primary alkyl radical having at least three carbon atoms, optionally containing a heteroatom, and R2 is a secondary alkyl or cycloalkyl radicals different from i-propyl, optionally containing a heteroatom. The catalysts obtained by using as internal electron-donor compound the said 1,3-diethers display in the (co)polymerization of olefins an excellent balance of activity and stereospecificity that cannot be reached with the ethers known in the art.