Catalyst components for the polymerization of olefins comprising Mg, Ti, halogen and 1,3-diethers as internal donors having an improved balance of properties in terms of activity and morphological stability are obtained by a process comprising: (A) A first step comprising reacting an adduct of formula MgCl2(ROH)n, where R is a C1-C10 alkyl group, and n is from 0.5 to 6, with a titanium compound having at least a Ti—Cl bond at a reaction temperature ranging from 0° C. to 80° C.; (B) A subsequent step comprising contacting the solid product obtained in (A) with an electron donor ED selected from 1,3 diethers with a titanium compound having at least a Ti—Cl bond at a temperature higher than 80° C.; and (C) A subsequent step comprising reacting the solid product coming from (B) with a titanium compound having at least a Ti—Cl bond at a temperature higher than 80° C.