Copolymerization of ethylene and styrene in the presence of the catalytic system η5-C5Me5Ti(CH2Ph)3−B(C6F5)3 has been investigated. Independently from the feed composition, basically alternating ethylene−styrene copolymers are obtained, together with some polyethylene and syndiotactic polystyrene, from which the former can be separated by solvent extraction. NMR analysis of suitably 13C-enriched end groups shows that the regiospecificity of styrene insertion in the initiation step is largely secondary. A tentative explanation for the preferentially alternating comonomer incorporation is proposed.