Catalyst components component for the (co)polymerization of olefins CH2═CHR, in which R is a hydrocarbyl radical with 1-12 carbon atoms, optionally in mixture with ethylene, comprising Ti, Mg, Zn, Cl, and an electron donor compound characterized by the fact that more than 50% of the titanium atoms are in the +4 valence state, and that the amount of Zn ranges from 0.1 to 4% by weight based on then total weight of said solid catalyst component.