Polymerizations of vinyl-cyclohexane (VCH) in the presence of catalytic systems based on zirconocenes belonging to C-2, C-2 or C-s symmetry group were performed. All polymers were analyzed by C-13 NMR spectroscopy and show isotactic microstructure. A steric control mechanism, involving a like 1,3-asymmetric induction of the chiral carbon of the last inserted unit on the chirality of the incoming monomer coordination, is proposed. This would be the only stereocontrol mechanism in the presence of a C-2-symmetry catalyst, and it would enforce or overcome site control in case of active species with C-2 and C-s-symmetry, respectively. (c) 2006 Elsevier Ltd. All rights reserved.