Ring-opening polymerization of the all-trans isomer of 1,2,3,4-tetramethyl-1,2,3,4-tetraphenylcyclotetrasilane (1) using (PhMe(2)Si)(2)Cu(CN)Li-2 affords nearly quantitative conversion to polymer with 75% heterotactic and 25% isotactic triads as determined by Si-29 NMR spectroscopy. Polymerization of a mixture of the stereoisomers of 1 leads to a polymer with 58% heterotactic, 15% syndiotactic, and 27% isotactic triads. The polymerization initiated with silyl cuprates occurs with inversion of configuration at both the attacked silicon atom and the newly formed reactive center. The polymers have molecular weights up to 30 000 depending on the ratio of [M](o)/[I](o) with M(w)/M(n) greater than or equal to 1.5. Kinetic measurements show a first-order dependence on monomer concentration and also on initiator concentration.